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Sertularella contorta Kirchenpauer, 1884 (Fig. 4E–H) Sertularella contorta.— Galea et al. 2017: 268–271, figs 1E–G, 6, 7A–H. ? Sertularella lagena Allman, 1876: 114; 1879: 283, text-fig.— Stechow, 1925: 475, fig. 34. Sertularella polyzonias.— Vanhöffen, 1910: 322 (in part). Material examined. PROTEKER 2: Baie Accessible, two masses of stems, with gonothecae (MNHN IK –2012– 10429). PROTEKER 3: Ile Suhn, several stems up to 80 mm high, with gonothecae, on Macrocystis (MNHN IK –2012–10424) and many stems, up to 30 mm high, with gonothecae, densely growing on Macrocystis (MNHN IK –2012–10425). Description. Stems monosiphonic with up to five basal annulations following the short stolonal apophyses. First annulation roughly transverse, the remaining rings distally ever more oblique. Branching generally alternate with no defined pattern. Branches up to third order observed. Branches usually originating frontally below a hydrotheca. Stem divided into short internodes arranged in a zigzag pattern. First branch internode of similar development. Internodes with a conspicuous basal swelling or “bourrelet” on hydrothecal side. Basal part of branches with an annulation formed by the apophysis giving rise to the branch, the basal swelling of the first hydrothecal internode and a ring (occasionally a few more) in between. Hydrothecae alternately arranged in two planes, usually making a very open angle, but sometimes either almost making a right angle or placed in the same plane. Hydrotheca adnate over one third of its adcauline length (Fig. 4E–H).Abcauline wall straight or slightly convex for most of its length, but curving outwards near the opening, making it concave (Fig. 4E–H). Free adcauline wall sigmoid, convex for most of its length, then concave below the aperture (Fig. 4E–H). Concave portion below the aperture of both adcauline and abcauline walls giving the appearance of a kind of neck. Rim with thickened perisarc, forming a sort of collar (Fig. 4E, H). Hydrothecal aperture with four cusps, abcauline one distinctly longer (Fig. 4E, G). Some polyps with a kind of short tentacles on their basal abcauline part (Fig. 4H). Gonothecae with two to four distal blunt cusps. Wall undulated at distal 1/2–2/3. Measurements (in µm). MNHN IK–2012–10429. Internodes: length 940–1100, diameter at hydrothecal base 420–440. Hydrothecae: length of abcauline wall 730–760, length free part of adcauline wall 490–500, length adnate part of adcauline wall 220–300, length adcauline wall 720–790, diameter at aperture 300–320. Gonothecae: length 1700, maximum diameter 900. Cnidome: microbasic mastigophores, range 5.8–6.5 x 1.7–2.0. MNHN IK-2012-10424. Internodes: length 970–1600, diameter at hydrothecal base 460–490. Hydrothecae: length of abcauline wall 690–780, length free part of adcauline wall 510–600, length adnate part of adcauline wall 290–300, length adcauline wall 810, diameter at aperture 280–320, maximum diameter 360–410. Gonothecae: length 2200–2260, maximum diameter 1000–1300. Cnidome: microbasic mastigophores, range 6.5–7.0 x 2.0. MNHN IK-2012-10425. Internodes: length 900–1200, diameter at hydrothecal base 500–530. Hydrothecae: length of abcauline wall 610, length free part of adcauline wall 500, length adnate part of adcauline wall 250, length adcauline wall 750, diameter at aperture 340, maximum diameter 440. Gonothecae: length 2200, maximum diameter 1000–1200. Cnidome: microbasic mastigophores, range 6.0–6.5 x 1.5–1.7. Remarks. Several species of Sertularella have been reported from Kerguelen. Allman (1876) poorly described three new species from the area, Sertularella kerguelensis Allman, 1876, Sertularella unilateralis Allman, 1876 and Sertularella lagena Allman, 1876, the first two found again by Studer (1879). Allman (1888) described another new species from this region, Sertularella secunda (Allman, 1888). Posteriorly, Vanhöffen (1910) reported Sertularella polyzonias (Linnaeus, 1758), Stechow (1925) S. lagena, Naumov & Stepanjants (1962) S. polyzonias and Millard (1977) Sertularella picta (Meyen, 1834). Galea et al. (2017), in their revision of the genus from southern South America and the sub-Antarctic, considered those records belonging to Sertularella allmani Hartlaub, 1901, Sertularella antarctica Hartlaub, 1901, Sertularella contorta Kirchenpauer, 1884 or Sertularella gaudichaudi (Lamouroux, 1824) (S. kerguelensis and S. lagena were considered nomina dubia). I have assigned the present material to Sertularella contorta with which it agrees the most, following the concept of the species by Galea et al. (2017), although it should be noted that they were unable to find, and therefore examine, type material of this species. The material studied here shares with Sertularella contorta the shape and size of the hydrothecae and internodes. According to Galea et al. (2017), the hydrothecae expand below the rim on both ab- and adcauline sides, which is also characteristic of the present material. In some material (MNHN IK–2012–10425) there are stout hydrothecae (Fig. 4F), as also depicted by Galea et al. (2017: fig. 6I), together with typical ones. Even when the general branching is alternate, there are numerous exceptions, much more so in the lower-order branches. As an example of branching, a stem (MNHN IK–2012–10429) with an alternate pattern was unbranched until its 10 th and 11 th internodes, with branches arranged alternately in two planes, making an acute angle. The stem alternately branches again at its 18 th, 21 st and 24 th internodes and successively at its 27 th, 28 th, 29 th and 30 th, but with exceptions (i.e. two branches on the same side). The primary branches also give rise to secondary branches alternately, starting at their 5 th or 6 th internode, but apparently without following a clear pattern (sometimes there are two hydrothecae in between, sometimes none). In another stem (MNHN IK–2012–10425), branching is alternate at the 2 nd, 3 rd and 4 th internodes, then on the same side (that of the 4 th internode) at the 6 th, and then on the opposite side at the 8 th, 10 th and 12 th (i.e. there is a hydrotheca in between). Subsequently, it changes again to the opposite side at its 13 th and 15 th internodes. In other material (MNHN IK–2012–10424) the profuse branching is best considered as irregular in several planes. The tendency to form two planes increases distally and the third-order branches are usually those forming an acute angle. In some places, subopposite pairs in more or less two planes are found; in others, branches are directed to the same side with one hydrotheca in between. The branching in the present material, as shown in the examples above, has nothing to do with the apparently more or less regular pinnate pattern described by Galea et al. (2017: 268), “with generally every two consecutive apophysis-bearing internodes separated by a couple of internodes not supporting side branches”. These authors, however, also described exceptions. The other noticeable difference is the absence of the three internal hydrothecal cusps that characterised the species according to Galea et al. (2017). Nonetheless, these authors also indicated that they may be absent. Even when Galea et al. (2017) indicated that the lateral cusps of the hydrothecal aperture are asymmetrical, I believe they are not. It is just a question of perspective. When observed from a perfect side view it is evident that they are equally developed. Ecology and distribution. Sertularella contorta was collected at depths between 14 and 48 m off Suhm Island and from Accessible Bay, on Macrocystis; gonothecae in December., Published as part of Peña Cantero, Álvaro L., 2022, On a few benthic hydroids (Cnidaria, Hydrozoa) from the Kerguelen Islands (southern Indian Ocean), including the description of a new species, pp. 274-286 in Zootaxa 5165 (2) on pages 282-285, DOI: 10.11646/zootaxa.5165.2.7, http://zenodo.org/record/6831887, {"references":["Kirchenpauer, G. H. (1884) Nordische Gattungen und Arten von Sertulariden. Abhandlungen und Verhandlungen Hamburg, 8 (3), 1 - 54.","Galea, H. R., Schories, D., Haussermann, H. & Forsterra, G. (2017) Taxonomic revision of the genus Sertularella (Cnidaria: Hydrozoa) from southern South America and the subantarctic, with the descriptions of five new species. Revue suisse de Zoologie, 124, 255 - 321.","Allman, G. J. (1876) Descriptions of some new species of Hydroida from Kerguelen's Island. Annals and Magazine of Natural History, Series 4, 17, 113 - 115. https: // doi. org / 10.1080 / 00222937608681913","Allman, G. J. (1879) Hydroida. In: An account of the petrological, botanical, and zoological collections made in Kerguelen's Land and Rodriguez during the transit of Venus Expeditions, carried out by order of Her Majesty's government in the years 1871 - 1875. Philosophical Transactions of the Royal Society of London, 168 (Extra Volume), 282 - 285.","Stechow, E. (1925) Hydroiden der Deutschen Tiefsee-Expedition. Wissenschaftliche ergebnisse der Deutschen Tiefsee-Expedition Auf Dem Damfper \" Valdivia \" 1898 - 1899, 17, 383 - 546.","Vanhoffen, E. (1910) Die Hydroiden der Deutschen Sudpolar-Expedition 1901 - 1903. Deutsche Sudpolar-Expedition 1901 - 1903, 11 (Zoology 3), 269 - 340.","Studer, T. (1879) Die Fauna von Kerguelensland. Verzeichniss der bis jetzt auf Kerguelensland beobachteten Thierspecies nebst kurzen Notizen uber ihr Vorkommen und ihre zoogeographischen Beziehungen. Archiv fur Naturgeschichte, 45, 104 - 141.","Allman, G. J. (1888) Report on the Hydroida dredged by H. M. S. Challenger during the years 1873 - 76. II. Tubularinae, Corymorphynae, Campanularinae, Sertularinae and Thalamophora. Report of the Scientific Results of the Voyage of H. M. S. Challenger 1873 - 1876, 70 (23), 1 - 90.","Linnaeus C. (1758) Systema naturae per regna tria natura, secundum classes, ordines, genera, species cum characteribus, differentiis, synonymis, locis. Editio decima, reformata. L. Salvii, Holmiae, 823 pp. https: // doi. org / 10.5962 / bhl. title. 542","Naumov, D. V. & Stepanjants, S. D. (1962) Hydroida (Thecaphora) collected by the Soviet Antarctic Expedition on the M / V Ob in antarctic and subantarctic waters. In: Biological results of the Soviet Antarctic Expedition, 1955 - 1958, 1. Issledovaniya Fauny Morei, 1 (9), 68 - 106.","Millard, N. A. H. (1977) Hydroids from the Kerguelen and Crozet shelves, collected by the cruise MD. 03 of the Marion-Dufresne. Annals of the South African Museum, 73 (1), 1 - 47.","Meyen, F. J. F. (1834) Uber das Leuchten des Meeres und Beschreibung einiger Polypen und anderer niederer Thiere. In: Beitrage zur Zoologie, gesammelt auf einer Reise um die Erde. Verhandlungen der Kaiserlichen Leopoldinisch-Carolinischen Akademie der Naturforscher, 16 (Supplment), 125 - 216.","Hartlaub, C. (1901) Revision der Sertularella Arten. Abhandlungen aus dem Gebiete der Naturwissenschaften, 16, 1 - 143.","Lamouroux, J. V. F. (1824) Description des polypiers flexibles. In: Quoy, J. R. C. & Gaimard, J. P. (Eds.), Voyage autour du monde, entrepris par ordre du Roi, execute sur les corvettes de S. M. l'Uranie et la Physicienne, pendant les annees 1817, 1818, 1819 et 1820. Zoologie, Pillet Aine, Paris, pp. 603 - 643."]}

Tubularia sp. (Fig. 3F) ? Tubularia indivisa.— Vanhöffen, 1910: 278–279, fig. 3. Material examined. PROTEKER 2: Ile Suhm, several stems up to 50 mm high, with gonophores (MNHN IK – 2012–10432). PROTEKER 3: Ile Shum, several stems up to 45 mm high, with immature gonophores (MNHN IK –2012–10427). Description. Stems up to 50 mm high, whitish (yellowish at the most basal part), thin, diameter only slightly increasing distally. Perisarc smooth, soft; softer and corrugated in the 3-mm-long neck region. Transparent perisarc film starting just below the polyp. Distinct constriction between polyp and neck region. Hydrocaulus with one larger and nine smaller peripheral longitudinal canals. Polyp white (Fig. 3F), small, about 4 mm high and 3 mm wide. Polyp’s column relatively long. Hydranth with a whorl of about 20 aboral filiform tentacles (three or four originating from an inner position) and around 30 tentacles on hypostome column: ten or so oral tentacles, roughly in a circle; the remaining below, apparently in one level and partially fused to the polyp column for a significant proportion. Some polyps with about eight unbranched blastostyles in a whorl just above the aboral tentacles. Blastostyles of different length, the longest with up to ten gonophores (Fig. 3F): the two or three most basal ones incipient, the others much more developed. Gonophores up to 500 µm high and 450 µm in diameter, pedicel about 200 µm long. Cnidome (from MNHN IK–2012–10432) consisting of larger stenoteles [12.7±0.5 x 12.6±0.8 µm (n= 10), range 12–13.5 x 11–13.5 µm], smaller stenoteles [8.2±0.6 x 6.7±0.8 µm (n= 10), range 7.5–9.0 x 6.0–7.0 µm], haplonemes [12.8±0.9 x 4.6±0.6 µm (n= 10), range 12–14.5 x 4.0–5.5 µm], and desmonemes 6 x 5 µm. Remarks. The material from MNHN IK–2012–10432 is in poor condition and it is not possible to count accurately the number of tentacles, let alone the oral ones, but there seems to be also 20 aboral tentacles. The polyps from MNHN ID–2012–10427 are in much better condition, yet the gonophores are barely developed. The present material cannot be fully characterised due to the incomplete development of the gonophores. Studer (1879) described as Tubularia ? kerguelensis a tubulariid from Kerguelen with smooth stems up to 3 cm. The present material is clearly distinguishable from it because Studer’s species had fewer oral tentacles (eight) than aboral ones (16). His material also lacked gonophores. Vanhöffen (1910) reported Tubularia indivisa Linnaeus, 1758 from Kerguelen. The present material is morphologically close to Vanhöffen’s and could certainly be conspecific. According to him, the stems, 30–40 mm high, are smooth, without any annulation, and have clear longitudinal streaks. The polyp has 30–40 oral tentacles, arranged in several rows, and about 20 aboral ones. Even if the present material was conspecific with the material assigned to T. indivisa by Vanhöffen (1910), it is not clear whether it actually belongs to this species. According to Petersen (1990), T. indivisa has stems up to 200 mm long, with firm perisarc, and the polyps have 40–60 oral tentacles. As indicated above, the present material has much shorter stems with soft perisarc and the number of oral tentacles is distinctly smaller. Vanhöffen’s material lacked gonophores and the gonophores in the present material are not completely developed. Therefore, it would be necessary to study well-preserved, mature material from the area to confirm the identification. Ecology and distribution. Tubularia sp. was collected at depths from 14 to 43 m off Suhm Island., Published as part of Peña Cantero, Álvaro L., 2022, On a few benthic hydroids (Cnidaria, Hydrozoa) from the Kerguelen Islands (southern Indian Ocean), including the description of a new species, pp. 274-286 in Zootaxa 5165 (2) on pages 280-281, DOI: 10.11646/zootaxa.5165.2.7, http://zenodo.org/record/6831887, {"references":["Vanhoffen, E. (1910) Die Hydroiden der Deutschen Sudpolar-Expedition 1901 - 1903. Deutsche Sudpolar-Expedition 1901 - 1903, 11 (Zoology 3), 269 - 340.","Studer, T. (1879) Die Fauna von Kerguelensland. Verzeichniss der bis jetzt auf Kerguelensland beobachteten Thierspecies nebst kurzen Notizen uber ihr Vorkommen und ihre zoogeographischen Beziehungen. Archiv fur Naturgeschichte, 45, 104 - 141.","Linnaeus C. (1758) Systema naturae per regna tria natura, secundum classes, ordines, genera, species cum characteribus, differentiis, synonymis, locis. Editio decima, reformata. L. Salvii, Holmiae, 823 pp. https: // doi. org / 10.5962 / bhl. title. 542","Petersen, K. W. (1990) Evolution and taxonomy in capitate hydroids and medusae. Zoological Journal of the Linnean Society, 100, 101 - 231. https: // doi. org / 10.1111 / j. 1096 - 3642.1990. tb 01862. x"]}

Coryne pusilla Gaertner, 1774 (Fig. 3A–B) ? Coryne conferta Allman, 1876: 115; 1879: 285, pl. 18 figs 1–3.— Studer, 1879: 121.— Vanhöffen, 1910: 274–275, fig. 1. Material examined. PROTEKER 3: Ile Suhm, a tuft of stems up to 25 mm high, with gonophores (MNHN IK –2012–10428). Description. Stems up to 25 mm high, unbranched or with only a few secondary stems (one stem gives rise to seven secondary stems and some of these to one, on one occasion two, third-order stems). Degree of stem annulation variable, but in general stems strong and densely ringed, smooth distally. No distal perisarc collar. Polyps with around 36 tentacles; five in a whorl around hypostome (Fig. 3A), the remaining with no clear arrangement. One or two little-developed gonophores present in a few polyps, originating at axil of basal tentacles. Gonophores roughly spherical, attached by a small pedicel to hydranth body. One 340 µm high and 270 µm in maximum diameter; another 240 µm in diameter. Cnidome consisting of stenoteles in two size classes (Fig. 3B): larger 20.1±1.1 x 12.9±0.7 µm (n= 10), range 18–22 x 12.0–14.0 µm, smaller 12.3±0.5 x 7.5±0.4 µm (n= 10), range 11.5–13.0 x 6.5–8.0 µm. Remarks. Allman (1876) described Coryne conferta n. sp. from Kerguelen. His brief description, based on infertile material, precludes assigning any material to this species. The present material could be conspecific with Allman’s, agreeing in general with the few characters he described, but the species is not sufficiently characterised. Schuchert (2001) already considered C. conferta an insufficiently described species, being indistinguishable from C. pusilla or Coryne eximia Allman, 1859. Coryne conferta was again reported from Kerguelen, also based on infertile material, by Studer (1879) and Vanhöffen (1910); the latter from the same locality as Allman’s material. I have assigned the present material to Coryne pusilla because it agrees with this species in the colony habit, the lack of perisarc collar at the end of the stem, the number of tentacles on the polyp and the size of the nematocysts. According to Schuchert (2001) the stems are 1–3 cm high, with five to 15 hydranths per shoot and rarely end in a funnel-shaped dilation; the polyps are provided with 18–28 tentacles. As for the size of the nematocysts, he reported stenoteles 18–23 x 11–15 µm and 12–16 x 6.5–10 µm. Schuchert (2001) indicated that Coryne pusilla was known from Kerguelen, but without providing a direct reference. He probably refers to Vanhöffen’s (1910: 275) record, which was described just after his record of C. conferta from Kerguelen. Schuchert (2001: 849) stated that “ Vanhöffen (1910) described infertile Coryne conferta colonies from close to the type locality and also fertile colonies of Coryne pusilla on floating Fucus ”. Even when Vanhöffen’s material of C. pusilla was collected on Fucus, as Schuchert indicated, it does not come from Kerguelen, but from the English Channel. Therefore, if confirmed, the present material would represent the first record of C. pusilla in the study area. Ecology and distribution. Coryne pusilla was collected at a depth of 14 m off Suhm Island., Published as part of Peña Cantero, Álvaro L., 2022, On a few benthic hydroids (Cnidaria, Hydrozoa) from the Kerguelen Islands (southern Indian Ocean), including the description of a new species, pp. 274-286 in Zootaxa 5165 (2) on page 278, DOI: 10.11646/zootaxa.5165.2.7, http://zenodo.org/record/6831887, {"references":["Gaertner, J. (1774) Zoophyta, quaedam minuta. In: Pallas, P. S., Specilegia Zoologia. Fasc. 10. G. A. Lange, Berolini, pp. 24 - 41.","Allman, G. J. (1876) Descriptions of some new species of Hydroida from Kerguelen's Island. Annals and Magazine of Natural History, Series 4, 17, 113 - 115. https: // doi. org / 10.1080 / 00222937608681913","Allman, G. J. (1879) Hydroida. In: An account of the petrological, botanical, and zoological collections made in Kerguelen's Land and Rodriguez during the transit of Venus Expeditions, carried out by order of Her Majesty's government in the years 1871 - 1875. Philosophical Transactions of the Royal Society of London, 168 (Extra Volume), 282 - 285.","Studer, T. (1879) Die Fauna von Kerguelensland. Verzeichniss der bis jetzt auf Kerguelensland beobachteten Thierspecies nebst kurzen Notizen uber ihr Vorkommen und ihre zoogeographischen Beziehungen. Archiv fur Naturgeschichte, 45, 104 - 141.","Vanhoffen, E. (1910) Die Hydroiden der Deutschen Sudpolar-Expedition 1901 - 1903. Deutsche Sudpolar-Expedition 1901 - 1903, 11 (Zoology 3), 269 - 340.","Schuchert, P. (2001) Survey of the family Corynidae (Cnidaria, Hydrozoa). Revue suisse de Zoologie, 108 (4), 739 - 878. https: // doi. org / 10.5962 / bhl. part. 80165","Allman, G. J. (1859) Notes on the hydroid zoophytes. Annals and Magazine of Natural History, Series 3, 4, 137 - 144. https: // doi. org / 10.1080 / 00222935908697098"]}

Candelabrum bitentaculatum sp. nov. (Figs 1–2) Material examined. Holotype: PROTEKER 2: Baie Philippe, one polyp 108 mm long, with gonophores (MNHN IK –2012–10431). Description. Hydranth about 108 mm long, with an 8 mm-long basal part, a gonophore-bearing middle part, about 40 mm long, and a 60 mm-long distal part provided with hundreds of capitate tentacles (Fig. 1A). Mature blastostyles unbranched, short, with up to six distal capitate tentacles and up to three basal, spherical gonophores in close proximity (Fig. 1B–E). The most basal gonophore barely developed, the others mature (Fig. 1D). Number of tentacles on blastostyles without gonophores ranging from a single distal tentacle to six (Fig. 1B– E). A few gonophores, the most distal ones, arising directly from the polyp’s body wall between normal tentacles (Fig. 1F). Hydranth basal part with blastostyle-like structures with four distal capitate tentacles, but also with five sucker tentacles below, forming a sort of crown (Fig. 1G–H). Some of the sucker tentacles with a small piece of perisarc (Fig. 1H). Cnidome (Fig. 2) consisting of microbasic euryteles [22.6±1.1 x 8.9±0.5 µm (n= 10), range 21–24 x 8–10 µm],?mastigophores [20.1±0.9 x 6.3±0.3 µm (n= 10), range 19–21.5 x 6–6.5 µm], larger desmonemes [13.1±0.2 x 10.1±0.2 µm (n= 10), range 13 x 10–10.5 µm], smaller desmonemes [9.3±0.4 x 6.4±0.3 µm (n= 10), range 9–10 x 6–7 µm] and stenoteles [11±0.0 x 9±0.0 µm (n= 10), range 11 x 9 µm]. Remarks. Although the area below the gonophore-bearing blastostyles extends over the basal eight millimetres, the blastostyle-like structures described above, provided with both capitate and sucker tentacles, only extent over the most basal five millimetres. If the presence of these sucker tentacles defined the basal part of the polyp, it then would be shorter, only five millimetres long. The isolated gonophores arising directly from the hydranth body wall between tentacles (Fig. 1F), above the blastostyle area, might represent male gonophores. If this were the case, the species would be monoecious. Candelabrum bitentaculatum sp. nov. differs from all known species of the genus by the unique blastostyle-like structure of the basal part of the polyp. From the southern hemisphere Candelabrum species, Candelabrum bitentaculatum sp. nov. also differs in several important features, mainly concerning the gonophore-bearing blastostyles. By having unbranched blastostyles, the present species differs from Candelabrum harrisoni (Briggs, 1928), whose blastostyles have an irregularly lobed base, from Candelabrum penola (Manton, 1940), which has irregularly lobed or branched blastostyles, and from Candelabrum meridianum (Briggs, 1938), whose blastostyles are branched. In the arrangement of the blastostyles, which have no defined pattern, Candelabrum bitentaculatum sp. nov. differs from Candelabrum capensis (Manton, 1940) and C. tentaculatum (Millard, 1966), in which the blastostyles are arranged in a single whorl. In the number of gonophores per blastostyle, Candelabrum bitentaculatum sp. nov. also differs from most species. As indicated above, there are only three gonophores, the most basal one barely developed. By contrast, in the species considered, the number of gonophores is higher. Thus, Candelabrum australe (Briggs, 1928) has three to four mature and six to eight immature gonophores, C. penola has up to 10 gonophores, C. capensis nine and C. tentaculatum and Candelabrum valdiviensis Galea & Schories, 2014 up to eight. Even Candelabrum austrogeorgiae (Jäderholm, 1904), whose blastostyles usually have one to three gonophores, has been observed with up to six gonophores per blastostyle. In the number of tentacles on the blastostyles, Candelabrum bitentaculatum sp. nov., which has up to six distal tentacles, differs from C. meridianum, which has none, and C. harrisoni, which has only one distal tentacle. Candelabrum austrogeorgiae has either a single stout, elongated tentacle at the tip, or a few smaller, weakly developed ones. On the other end, C. tentaculatum has about 25 tentacles. By its naked basal part, Candelabrum bitentaculatum sp. nov. also differs from C. harrisoni, in which the basal part is covered with perisarc. Vanhöffen (1910) reported Candelabrum austrogeorgiae (as Myriothela Austro-georgiae) from Kerguelen, indicating that his material coincided completely with the upper part of the specimen depicted by Jäderholm (1905, pl. 2, fig. 1). However, Vanhöffen’s material consisted of a 10-mm-long fragment corresponding to the most distal part of a polyp, with about 40 rows of densely packed, capitate tentacles. In the light of the present results, it is plausible to consider that Vanhöffen’s material could actually belong to Candelabrum bitentaculatum sp. nov., which also has a distal part provided with hundreds of capitate tentacles. Ecology and distribution. Candelabrum bitentaculatum sp. nov. was collected at a depth of 102 m in Philippe Bay; gonophores in November. Etymology. The specific name bitentaculatum refers to the presence of two types of tentacles, capitate and sucker-tentacles, in the blastostyle-like structures of the hydranth basal part., Published as part of Peña Cantero, Álvaro L., 2022, On a few benthic hydroids (Cnidaria, Hydrozoa) from the Kerguelen Islands (southern Indian Ocean), including the description of a new species, pp. 274-286 in Zootaxa 5165 (2) on pages 275-278, DOI: 10.11646/zootaxa.5165.2.7, http://zenodo.org/record/6831887, {"references":["Briggs, E. A. (1928) Studies in Australian athecate hydroids. I. Two new species of the genus Myriothela. Records of the Australian Museum, 16 (7), 305 - 315. https: // doi. org / 10.3853 / j. 0067 - 1975.16.1928.792","Manton, S. M. (1940) On two new species of the hydroid Myriothela. Scientific Reports of the British Graham Land Expedition, 1 (4), 255 - 293.","Briggs, E. A. (1938). Hydroida. Scientific Report of the Australasian Antarctic Expedition 1911 - 1914, 9 (4), 1 - 46, pls. 15 - 16.","Millard, N. A. H. (1966) The Hydrozoa of the south and west coasts of South Africa. Part III. The Gymnoblastea and small families of the Calyptoblastea. Annals of the South African Museum, 48 (18), 427 - 487.","Galea, H. R., Schories, D., Forsterra, G. & Haussermann, V. (2014) New species and new records of hydroids (Cnidaria: Hydrozoa) from Chile. Zootaxa, 3852 (1), 1 - 50. https: // doi. org / 10.11646 / zootaxa. 3852.1.1","Jaderholm, E. (1904) Mitteilungen ueber einige von der Schwedischen Antarctic-Expedition 1901 - 1903 eingesammelte Hydroiden. Archives de Zoologie Experimentale et Generale, Series 4, 3 (Notes et Revue 1), 1 - 14.","Vanhoffen, E. (1910) Die Hydroiden der Deutschen Sudpolar-Expedition 1901 - 1903. Deutsche Sudpolar-Expedition 1901 - 1903, 11 (Zoology 3), 269 - 340.","Jaderholm, E. (1905) Hydroiden aus antarktischen und subantarktischen Meeren, gesammelt von derschwedischen Sudpolarexpedition. Wissenschaftliche Ergebnisse der Schwedischen Sudpolar-Expedition 1901 - 1903, 5 (8), 1 - 41."]}

Schizotricha trinematotheca Peña Cantero & Vervoort, 2005 Schizotricha trinematotheca Peña Cantero & Vervoort, 2005: 809–812, fig. 2; Peña Cantero, 2009: 1747, fig. 2g –h. Material examined. TAN 0602/420, one stem 85 mm high and another at least 130 mm high, with immature gonothecae (NIWA 144243); TAN 0602/422, one stem 90 mm high (NIWA 144252); TAN 0602/430, one stem 230 mm high, with gonothecae (NIWA 144249). Remarks. In the present material cauline internodes are provided with three infrahydrothecal nematothecae and, sometimes, one suprahydrothecal nematotheca. Intermediate ahydrothecate internodes, following cauline and hydrocladial apophyses, are provided with two to three nematothecae. Unforked hydrocladial internodes with two to four infrahydrothecal nematothecae and one to two suprahydrothecal nematothecae. Double internodes with three nematothecae below first hydrotheca, three nematothecae between both hydrothecae and one nematotheca above second hydrotheca. As typical, hydrocladia very long, with up to 47 hydrothecae. Ecology and distribution. Schizotricha trinematotheca has been collected at depths from 70 to 579 m, on stones and gravel (Peña Cantero 2009); present material between 70 and 315 m. Gonothecae in February (Peña Cantero & Vervoort 2005) and March (Peña Cantero 2009; present material). Peña Cantero & Vervoort (2005) reported it from off Buckle Island and Peña Cantero (2009) off Sturge, Buckle and Young islands; present material off Sturge and Buckle islands. Until the study by Peña Cantero (2019), who reported it from a seamount off Scott Island, it was considered endemic to the Balleny Islands.

Symplectoscyphus sp. (*) Symplectoscyphus sp. Peña Cantero, 2009: 1749, fig. 3f. Remarks. Peña Cantero (2009) pointed out the similarity of his material to Symplectoscyphus glacialis (Jäderholm, 1904), but kept it to genus level because the material was deprived of gonothecae. The material had been collected at depths from 96 to 117 m off Sturge Island., Published as part of Peña Cantero, Álvaro L., 2021, Additions to knowledge of the biodiversity of benthic hydroids (Cnidaria: Hydrozoa) in the Balleny Islands (Antarctica), pp. 321-336 in Zootaxa 4966 (3) on page 329, DOI: 10.11646/zootaxa.4966.3.4, http://zenodo.org/record/4736691, {"references":["Pena Cantero, A. L. (2009) Benthic hydroids (Cnidaria, Hydrozoa) from the Balleny Islands (Antarctica). Polar Biology, 32, 1743 - 1751. https: // doi. org / 10.1007 / s 00300 - 009 - 0673 - 7","Jaderholm, E. (1904) Mitteilungen ueber einige von der Schwedischen Antarctic Expedition 1901 - 1903 eingesammelte Hydroiden. Archives de Zoologie Experimentale et Generale, Series 4, 3 (Notes et revue 1), 1 - 14."]}

Antarctoscyphus elongatus (Jäderholm, 1904) (Fig. 1H) Material examined. TAN 0102/K0809, one basally broken stem 90 mm long (NIWA 144358); TAN 0602/430, one stem 85 mm high (NIWA 144242). Ecology and distribution. Present material, which represents the first record of this species from the Balleny Islands, collected at depths from 70 to 292 m, off Young and Buckle islands.

Oswaldella vervoorti Peña Cantero & García Carrascosa, 1998 (Figs 3–4) Oswaldella sp. Peña Cantero, 2009: 1749, fig. 3c. Material examined. TAN 0602/430, one stem 90 mm high, with gonotheca (NIWA 144249), one stem 50 mm high, with gonothecae (NIWA 144253) and one stem 50 mm high (NIWA 144255). Description. Stems up to 90 mm high, monosiphonic, divided into internodes (one or two apophyses per internode). Cauline apophyses alternately arranged in one plane, with two axillary nematophores and one mamelon (Fig. 3F). Cauline apophyses giving rise to hydrocladia with a distinct separation between them. Up to second order hydrocladia present. Hydrocladia divided into internodes. Unforked hydrocladial internodes (Fig. 3A–B, G) with one hydrotheca on distal half of internode and two nematophores: a mesial superior nematophore, placed behind free part of adcauline hydrothecal wall (Fig. 3E), and a mesial inferior nematophore, situated on a slightly raised part of the internode and provided with a reduced scale-shaped nematotheca (Fig. 3C–D, H). Forked hydrocladial internodes with hydrotheca between two prongs, each of them with a nematophore, and one mesial inferior nematophore provided with a scaleshaped nematotheca. Apophyses supporting lower-order hydrocladia usually smaller than distal part of internodes. Hydrotheca slightly higher than wide. Adnate to internode for about three-fourths of its adcauline length. Hydrothecal basal part distinctly oblique; abcauline side lower. Abcauline hydrothecal wall longer than adcauline side, aperture slightly directed adcaudally. Distal third of abcauline wall distinctly directed outwards (Fig. 3C–D, H). Gonotheca elongated, club-shaped (Fig. 3I). Measurements (in µm). Hydrotheca: length of abcauline wall from 200 µm at 1 st internode to 300 µm at 7 th, free part of adcauline length 50, diameter at aperture 230–250. Gonothecae: length 2000, maximum diameter 480–700. Nematocysts: larger microbasic mastigophores, 11–12.5 x 3–3.5. Remarks. One of the 50-mm-high stems (NIWA 144253) is provided with a secondary stem originating from a forked hydrocladial internode at the usual location of the gonothecal insertion. This second-order stem has a typical structure. Most cauline apophyses of the 90-mm-high stem are deprived of mamelons; a little prominent mamelon was observed only twice. In one of the 50-mm-long stems (NIWA 144255) only some apophyses, particularly at the basal part of the stem, also present mamelon. In the material studied most hydrocladia are either unforked or just bifurcated (the first internode of primary hydrocladia giving rise to a single secondary hydrocladium). In one of the 50-mm-long stems (NIWA 144255) only seven of its last eight hydrocladia are bifurcated with apophyses quite similar to the distal part of the internode and the hydrotheca approximately in the middle of the bifurcation. There are, however, signs of other branching below. In one case, one first-order hydrocladium has the basal part of four secondary ones, one on each of its four first internodes, resting on distinctly smaller apophyses situated laterally under the hydrotheca. On a few occasions there are secondary hydrocladia that do not originate from the first internodes of the primary hydrocladium, but from others (i.e. there are unforked hydrothecate internodes before the forked ones). This material (NIWA 144255) has hydrothecae (Fig. 3G–H) less elongated (abcauline length up to 250 µm) and wider (diameter at aperture up to 280 µm) than those from the remaining material (Fig. 3A–D). It also has some nematothecae clearly more developed, with a distinct adcauline wall (Fig. 3H). This material, however, is the closest to O. vervoorti by the branching, with unforked hydrothecate internodes between forked ones. According to Peña Cantero & García Carrascosa (1998), although lower-order hydrocladia typically arise from the first internodes of the primary hydrocladia, in many cases unforked hydrothecate internodes were present preceding forked ones. On the other hand, looking at their figures (cf. fig. 1a–c in Peña Cantero & García Carrascosa 1998) it is evident that the apophyses supporting lower-order hydrocladia are smaller than the distal part of the internode. Clearly, it is not a simple bifurcation of the internode. Instead, it is like a normal hydrothecate internode laterally giving rise to the lower-order hydrocladium. In order to confirm this point, I have examined the holotype of O. vervoorti. The first forked hydrocladial internode is the most misleading as sometimes the apophysis supporting the second-order hydrocladium is similar to the distal part of the internode (Fig. 4A); in addition, both the apophysis and the distal part of internode are provided with a nematophore placed at approximately the same level. In all the remaining forked hydrocladial internodes, the prongs are markedly dissimilar (Fig. 4B), one is clearly the distal part of the internode, the other is undoubtedly the apophysis. Both are also provided with nematophores, but that of the apophysis is placed at a lower level (Fig. 4B). The first internodes originating from the apophyses are relatively very long (up to 1300 µm) (Fig. 4C). The primary hydrocladium might give rise to several second-order hydrocladia (up to six according to Peña Cantero & García Carrascosa 1998). Most secondary hydrocladia originate sequentially from the first (up to the fourth) internodes of the primary one, but it is not unusual to observe extra secondary hydrocladia originating after some unforked internodes (this is clearly shown in figure 1a in Peña Cantero & García Carrascosa 1998). The first secondary hydrocladium usually gives rise to a third-order hydrocladium at its first internode, but it can also form other tertiary hydrocladia (up to three according to Peña Cantero & García Carrascosa 1998), sometimes also beyond unforked internodes (see also figure 1a in Peña Cantero & García Carrascosa 1998). According to these authors, the first third-order hydrocladium sometimes even forms a fourth-order one. Mamelons are more prominent in the holotype than in the present material (compare Fig. 3F with Fig. 4E). Although suspicious on geographic grounds, there is no evidence to consider the material studied here different from O. vervoorti. This would not be the first Antarctic benthic hydroid previously considered endemic to West Antarctica and later found in East Antarctica. Peña Cantero (2009) reported, as Oswaldella sp., material likely conspecific with the one studied here, which is considered to belong to O. vervoorti. The young stems, up to 20 mm high, are divided into internodes with one or two apophyses each, the hydrocladia are unforked and the cauline apophyses are provided with two axillary nematophores and the most distal ones have mamelon. The size of the hydrotheca also agrees. Ecology and distribution. Present material was collected at depths between 70 and 120 m off Buckle Island; gonothecae in March. The material described as Oswaldella sp. by Peña Cantero (2009) came from a depth of 70–85 m off Buckle Island. Not only is O. vervoorti reported for the first time from the area of study, but also for East Antarctica, which indicate that its geographical distribution may be considered as circum-Antarctic.

Abietinella operculata (Jäderholm, 1903) (*) Abietinella operculata — Peña Cantero, 2009: 1747. Remarks. Known off Sturge Island, at depths between 640 and 702 m (Peña Cantero 2009).

‘ Bougainvilliidae undetermined’(*) ‘ Bougainvilliidae undetermined’ Peña Cantero, 2009: 1744. Remarks. Peña Cantero (2009) reported this species off Sturge Island, on Symplectoscyphus sp., at depths from 96 to 117 m. It could not be identified given the scarcity and infertile condition of the material.

Staurotheca pachyclada (Jäderholm, 1904) (*) Staurotheca pachyclada — Peña Cantero, 2009: 1479, fig. 3e. Remarks. Peña Cantero (2009) reported this hydroid at depths between 103 and 151 m off Young Island; gonothecae in March.

Halecium interpolatum Ritchie, 1907 (Figs 5 G–J, 8 A–B) Halecium interpolatum Ritchie, 1907: 526, pl. 1 fig. 3, pl. 2 fig. 3; Rees & Thursfield, 1965: 107, 197; Smaldon, Heppell & Watt, 1976: 17; Stepanjants, 1979: 103, pl. 16 fig. 7; Blanco, 1994 a: 156; 1994 b: 186; Vervoort & Watson, 2003: 86; Watson, 2008: 171 –172, fig. 7 A, B. Halecium ovatum Totton, 1930: 143, fig. 3; Vervoort, 1972 b: 339, fig. 1; Stepanjants, 1979: 103, pl. 20 fig. 1 a–g; Blanco, 1994 a: 156; 1994 b: 187; Peña Cantero & García Carrascosa, 1995: 12 –13, fig. 2 G–H; 1999: 212 et seq.; Vervoort & Watson, 2003: 86; Peña Cantero, 2004: 769; 2008: 455, fig. 1 e–g; 2009: 1747, fig. 2 f; 2013: 128, fig. 3 e; Watson, 2008: 172 –173, fig. 8 A, B; Peña Cantero & Vervoort, 2009: 85, fig. 1 f; Galea & Schories, 2012 b: 9, fig. 2 J–K; Peña Cantero et al., 2013: 745–747, fig. 6 b. Halecium tenellum —Stepanjants, 1972: 72; Blanco, 1984: 10 –11, pl. 6 figs 14–15. Halecium tubatum Watson, 2008: 174 –175, fig. 10 A, B (in part). ? Halecium ovatum —Watson, 2003: 166, fig. 15 D, E. Material examined. Scottish National Antarctic Expedition 1902–1904: Scotia Bay, South Orkneys, 06– 12–1903; RSM 1921.143. 1328 Leptotype of H. interpolatum, several stems, up to 35 mm high [in addition, one microslide (1959.33.153) with one stem, c. 23 mm high]; RSM 1921.143.1328A, Paratype of H. interpolatum, several stems, up to 35 mm high. BANZARE [as H. tubatum by Watson (2008)], Stn 105, 67° 46 'S 67 °03'E (Mawson Coast), 13 –02– 1931, 163 m; two microslides (Hydr. 710 / 12): F 147470.2, a few incipient stems in bad condition, and F 147470.3, hydrorhiza with just two incipient stems. Spanish Antarctic Expedition Bentart 95 [H. ovatum by Peña Cantero (2008)]: Stn 27 A, several stems, up to 35 mm high, with gonothecae. New Zealand Antarctic Expedition TAN0402 [H. ovatum by Peña Cantero (2009)]: Stn 239 VV, an old, strongly polysiphonic stem, c. 22 mm high. Spanish Antarctic Expedition Bentart 2006 [H. ovatum by Peña Cantero (2013)]: Stn Low 44, several stems, up to 30 mm high; Stn Low 45, four stems, up to 17 mm high. Diagnosis. Basally polysiphonic, slightly geniculate stems, up to 35 mm high. Stem giving rise to paired branches originating from hydrophore of primary hydrotheca. Intenodes with a characteristic long and straight basal part, followed by one or two annulations. Hydrothecae alternately arranged in one plane. Hydrotheca at the end of free hydrophore. Hydrothecal diameter strongly increasing distally; rim everted. Gonothecae flattened, bivalve-shaped, developing from hydrotheca. Cnidome consisting of microbasic mastigophores? and microbasic euryteles? Description (type material of H. interpolatum). Stems up to 35 mm high, in very bad condition, deprived of coenosarc and overgrown by bryozoans over much of its extension. Stems slightly geniculate and weakly polysiphonic basally. Perisarc very fragile. Stems having lost most paired-branches, although their origin still visible (Figs 5 G, 8 A). Successive internodes forming at some distance below hydrothecae, which are consequently free (Fig. 8 A). Internodes with a distinct, long and straight basal part, usually interrupted distally, forming one or two rings far below hydrotheca. Internode complete in other occasions. Hydrothecae almost completely absent and in very bad condition. Hydrotheca strongly widening distally; rim everted (Fig. 8 B). Only one type of nematocyst could be observed. Measurements (in µm). Hydrothecae: diameter at aperture 210–280, diameter at diaphragm 130–150, height c. 80. Cnidome: microbasic euryteles? [range 10–10.5 x 5.5–6, mean 10.3 ± 0.3 x 5.6 ± 0.2 (n= 4); ratio, range 1.8–1.9, mean 1.8 ± 0.1 (n= 4)]. Remarks. The leptotype was designated by Rees & Thursfield (1965). Apart from Watson’s (2008) record, Halecium interpolatum has never been reported since the original description by Ritchie (1907). Apparently, however, it has been found again several times, but recorded as Halecium ovatum Totton, 1930. After examining the type material of Halecium interpolatum, I believe that H. ovatum is conspecific with this species. The type material of the latter has not been examined because it was studied by Vervoort (1972 b) and Watson (2008) who provided enough information to characterize this species. Moreover, abundant additional material (see material examined) was available from several Antarctic expeditions. Halecium ovatum agrees with H. interpolatum in the shape and size of hydrotheca, the peculiar colony structure and the cnidome. In spite of the bad condition of the leptotype, it is possible to observe the origin of paired branches as typically occurs in H. ovatum, as well as the peculiar structure of the internodes, with a long and straight basal part, usually interrupted distally and followed by one or two annulations. Ritchie (1907) already characterized this species by the presence of characteristic athecate intermediate internodes. In addition, according to Watson (2008) the cnidome of the holotype of H. ovatum includes a type of nematocyst, doubtfully considered by her as anisorhizas, of similar size (11–12 x 6–7 µm). Due to the bad condition of the type material of H. interpolatum (already pointed out by Ritchie), and the absence of coenosarc, I could observe only a few nematocysts, consisting of microbasic euryteles? Stepanjants (1979) already pointed out the great similarity between H. interpolatum and H. ovatum in colony branching and hydrothecal constitution, indicating that the only difference was the presence of lateral stolons in the branches of H. interpolatum. It should be noted, however, that Ritchie (1907: 526) stated that “One of the branches ended in peculiar, stolon-like outgrowths”. Stepanjants (1979), finally, indicated that future studies could allow considering both conspecific. She also brought to H. ovatum and, consequently, is brought to H. interpolatum here, the material previously considered by her (Stepanjants, 1972) as H. tenellum. Part of the material assigned to Halecium tubatum by Watson (2008), in particular the material from the slides F 147470.2 and F 147470.3 (see material examined), actually belong to H. interpolatum (cf. Fig. 5 H–J). Unfortunately no nematocysts were found. See the discussion below, when dealing with H. tubatum. The material assigned to H. tenellum by Blanco (1984) also appears to belong to H. interpolatum. Peña Cantero (2013) already indicated that it could belong to H. ovatum (here considered conspecific with H. interporlatum). They agree in size and shape of the hydrothecae, the presence of paired branches and the structure of the internodes (cf. pl. 6 in Blanco 1984). Ecology and distribution. Shelf species found at depths from three (Stepanjants 1979) to 471 m (Peña Cantero & García Carrascosa 1995). Frequently reported epibiotic on other species of hydroids (Totton 1930; Stepanjants 1979; Peña Cantero & García Carrascosa 1995; Peña Cantero 2008, 2013; Peña Cantero & Vervoort 2009), but also on algae (Peña Cantero et al. 2013), sponges (Stepanjants 1979), polychaete tubes (Totton 1930; Stepanjants 1979), and bryozoans (Peña Cantero 2013; Peña Cantero et al. 2013). Used in turn as substratum for other hydroids (Peña Cantero et al. 2013). Gonothecae in January (Totton 1930; Stepanjants 1979; Peña Cantero et al. 2013), February (Peña Cantero 2008; Galea & Schories 2012 b) and December (Stepanjants 1979). Circum-Antarctic distribution, reported from Scotia Bay, the South Orkney Islands (Ritchie 1907), Palmer Archipelago (Vervoort 1972 b), off Elephant Island (Peña Cantero & García Carrascosa 1995), Low Island (Blanco 1984; Peña Cantero & Vervoort 2009; Peña Cantero 2013), and from the South Shetland Islands (Peña Cantero 2008; Galea & Schories 2012 b), in West Antarctica, and from the Ross Sea (Totton 1930; Peña Cantero et al. 2013), Commonwealth Bay, George V Coast (Watson 2008), Mawson Coast (Watson 2008 as H. tubatum), the Davis Sea (Stepanjants 1972, 1979), and the Balleny Islands (Peña Cantero 2009), in East Antarctica.

Hydractinia sp. (*) Hydractinia sp. Peña Cantero, 2009: 1745. Remarks. Peña Cantero (2009) found Hydractinia sp. at depths between 640 and 702 m off Sturge Island, on E. generale, indicating that the infertile condition precluded the identification., Published as part of Peña Cantero, Álvaro L., 2021, Additions to knowledge of the biodiversity of benthic hydroids (Cnidaria: Hydrozoa) in the Balleny Islands (Antarctica), pp. 321-336 in Zootaxa 4966 (3) on page 323, DOI: 10.11646/zootaxa.4966.3.4, http://zenodo.org/record/4736691, {"references":["Pena Cantero, A. L. (2009) Benthic hydroids (Cnidaria, Hydrozoa) from the Balleny Islands (Antarctica). Polar Biology, 32, 1743 - 1751. https: // doi. org / 10.1007 / s 00300 - 009 - 0673 - 7"]}

Phialella belgicae (Hartlaub, 1904) (Fig. 1E) Material examined. TAN0602/420, a few hydrothecae, on Staurotheca glomulosa Peña Cantero, Svoboda & Vervoort, 1997 (NIWA 144240). Ecology and distribution. Present material, representing the first record of P. belgicae for the Balleny Islands, was collected at a depth of 103−108 m off Sturge Island, epibiotic on S. glomulosa.

Lafoea dumosa (Fleming, 1820) (Fig. 1D) Material examined. TAN 0602/442, a 12-mm-high stem (NIWA 144244). Remarks. The present material agrees with that frequently reported in Antarctic waters. The hydrotheca, provided with a ringed pedicel, is roughly 700 µm high and 150 µm in diameter at aperture. The isorhizas are around 22 x 9 µm, coinciding with one of the two morphotypes found by Schuchert (2001) in relation to the size of the isorhizas. Ecology and distribution. The material, which represents the first record of the species for the Balleny Islands, was collected at a depth of 140−150 m off Buckle Island.

Staurotheca glomulosa Peña Cantero, Svoboda & Vervoort, 1997 Staurotheca glomulosa — Peña Cantero & Vervoort, 2003: 2687–2689, fig. 9. Material examined. E220B, a a mass of stems 20 mm in diameter (NIWA 128457); TAN 0602/420, one colony 100 mm high, basibiont of P. belgicae (NIWA 144240). Measurements (in µm). Hydrotheca: abcauline wall 630–700, free part of adcauline wall 100–130, adnate part of adcauline wall 730–780, adcauline wall 830–910, diameter at aperture 230–270. Remarks. The planar colonies are polysiphonic and the presence of anastomoses gives them a mesh-shaped appearance. The hydrothecae are arranged in decussate pairs, forming four longitudinal rows. Ecology and distribution. Staurotheca glomulosa had been previously reported at depths between 55 and 157 m (Peña Cantero & Vervoort 2003); present material collected at depths from 103 to 371 m. Basibiont for colonies of P. belgicae (present material). Peña Cantero & Vervoort (2003) reported it off Buckle Island; present material found off Young and Sturge islands.

Symplectoscyphus cumberlandicus (Jäderholm, 1905) (Fig. 2A–B) Material examined. TAN 0602/420, three stems up to 10 mm high (NIWA 144240); TAN 0602/448, one stem 100 mm high, with gonothecae (NIWA 144241). Measurements (in µm). Hydrotheca: length abcauline wall 350–450, length free part of adcauline wall 140– 200, length adnate part of adcauline wall 370, length adcauline wall 510–570, diameter at aperture 160–200. Remarks. The polysiphonic stem, branched in one plane, and the shape and size of hydrothecae (Fig. 2A) and gonothecae (Fig. 2B), the latter with about 13 spirally arranged rings, make certain the identification of the material from TAN 0602/448. The material from TAN 0602/420, although consisting of small stems up to 10 mm high, also agrees in the shape and size of the hydrothecae. One of the stems has, in addition, a basal 3-mm-long stolon, pointing to the polysiphonic condition found in larger stems. Ecology and distribution. Present material, the first record of Symplectoscyphus cumberlandicus from the Balleny Islands, was collected at depths between 63 and 108 m off Young and Sturge islands. Gonothecae in material collected in March.

Stegella lobata (Vanhöffen, 1910) Material examined. E203, two stem fragments 50 and 55 mm long, with male gonothecae, basibiont of F. antarcticum (NIWA 128467). Remarks. Although only a few hydrothecae in bad condition are left, the typical colony structure allows a confident identification. The male gonotheca is roughly 1800 µm in height and 700 µm in maximum diameter. Ecology and distribution. The material, which represents the first record of the species for the Balleny Islands, was collected at a depth of 187 m off Sturge Island.

Hydrodendron arboreum (Allman, 1888) (*) Hydrodendron arboreum — Peña Cantero, 2009: 1747. Remarks. Reported off Sturge and Young islands, from depths between 96 and 127 m, growing on pebbles (Peña Cantero 2009).

Oswaldella incognita Peña Cantero, Svoboda & Vervoort, 1997 Oswaldella incognita — Peña Cantero, 2009: 1748–1749, fig. 3a. Material examined. TAN 0102/K0809, one stem 120 mm high, with gonothecae (NIWA 144358); TAN 0602/430, one stem 90 mm high, with only a few hydrocladia left, in bad condition (NIWA 144253), one stem 200 mm high, with gonothecae (NIWA 144250) and one stem 110 mm high, with just a few hydrocladia left (NIWA 144249); TAN 0602/436, one stem 80 mm high, with one gonotheca (NIWA 144257). Ecology and distribution. Previously known off Buckle Island, from depths between 70 and 584 m (Peña Cantero 2009). The material studied here was collected at depths from 70 to 292 m off Young and Buckle islands; gonothecae found in material collected in March.

Oswaldella bifurca (Hartlaub, 1904) (*) Oswaldella bifurca — Peña Cantero & Vervoort, 2004: 816–818, fig. 1. Remarks. Oswaldella bifurca is known off Buckle Island, where it was collected at a depth of 1442–1444 m (Peña Cantero & Vervoort 2004).

Halecium incertus Naumov & Stepanjants 1962 (Figs 6–7) Halecium incertus Naumov & Stepanjants, 1962: 98, fig. 18; Stepanjants, 1979: 107, pl. 20 fig. 7 A–V; Vervoort & Watson, 2003: 86; Peña Cantero, 2004: 769; Peña Cantero & Gili, 2006: 766. Halecium dufresnae Millard, 1977: 8, fig. 2 A–D; 1979: 138; Branch & Williams, 1993: 11, fig.; Vervoort & Watson, 2003: 85. Halecium macrocaulus Watson, 2008: 173 –174, fig. 9 A–F. Not Halecium incertus — Peña Cantero, 2008: 454 –455, fig. 1 b; 2009: 1747; 2012: 857 (= Halecium pseudoincertus sp. nov.). Material examined. Holotype of Halecium incertus, ZIRAS, “Ob” II SAE, Stn 204, 30–02–1957, 65° 59,2S 57 °08’ 8 E (Enderby Land), 270 m, three stem fragments, 42, 32 and 30 mm long, with gonothecae. Holotype of Halecium macrocaulus, BANZARE, Stn 107, 66° 45 'S 62 °03'E (Mawson Coast), 210 m, one microslide, NMV F 147467, one stem fragment, c. 24 mm long, with gonothecae. German Antarctic Expedition Polarstern XXI/ 2: Stn PS 65 /019, one stem, c. 195 mm high, with gonothecae. Diagnosis. Strongly polysiphonic, irregularly branched stems, up to 300 mm high. Branches originating from hydrophore of primary hydrotheca. Hydrothecae alternately arranged in one or two planes. Hydrotheca at the end of short, adnate hydrophore provided with oblique pseudodiaphragm. Hydrotheca distinctly widening distally; rim slightly everted. Adcauline hydrothecal wall free; distinctly larger than abcauline one. Hydrothecal aperture slightly directed downwards. Up to one secondary hydrotheca present. Male gonoteca oval, elongated with distal, shallow groove. Female gonotheca flattened, terebratulid brachiopod-shaped; abcauline wall longer. Aperture at distal part. With acrocyst (one embryo). Cnidome consisting of isorhizas, larger microbasic euryteles, smaller microbasic euryteles and microbasic mastigophores. Description (type material of H. incertus). Three stem fragments, c. 42, 32 and 30 mm long. 42 -mm-long fragment corresponding to a basal stem fragment, strongly polysiphonic, c. 3 mm in diameter, and provided with a primary branch, strongly polysiphonic too. Branches divided into internodes by alternately arranged, slightly oblique nodes. Hydrothecae on adnate hydrophores (Fig. 6 A–D); ratio between adcauline length of hydrophore and diameter at diaphragm 1.2–1.5. Hydrotheca low (Fig. 6 A–D), distinctly widening from diaphragm upwards. Adcauline wall distinctly larger than abcauline one (Fig. 6 A, D). Adcauline hydrothecal wall free to internode (Fig. 6 A–D). Hydrothecal aperture slightly directed downwards. Hydrothecal rim slightly everted (Fig. 6 A). Up to one secondary hydrotheca present (Fig. 6 A). An oblique, upwards directed pseudodiaphragm present (Fig. 6 A,D). Two female gonothecae present, arising from hydrophore of primary hydrotheca. Gonotheca fusiform, terebratulid brachiopod-shaped, with one side shorter (Fig. 6 E). Measurements (in µm). Hydrothecae: diameter at aperture 260–300, diameter at diaphragm 230–250, height 35–50. Internodes: length 550–700, diameter 210–300. Gonothecae: height c. 1350, maximum diameter c. 470. Cnidome: isorhizas [range 19.0– 21.5 x 6.0–8.0, mean 20.5 ± 0.7 x 7.2 ± 0.6 (n= 10); ratio, range 2.6–3.3, mean 2.9 ± 0.2 (n= 10)], larger microbasic euryteles?, very abundant [range 15.5 –18.0 x 6.0–8.0, mean 16.4 ± 0.7 x 7.3 ± 0.7 (n= 10); ratio, range 2.0– 2.7, mean 2.3 ± 0.2 (n= 10)], smaller microbasic euryteles [range 7.5 –8.0 x 4.0, mean 7.8 ± 0.2 x 4.0±0.0 (n= 10); ratio, range 1.9 –2.0, mean 2.0± 0.1 (n= 10)], and microbasic mastigophores [range 8.0– 8.5 x 2.0– 2.5, mean 8.3 ± 0.2 x 2.3 ± 0.2 (n= 10); ratio, range 3.2–4.3, mean 3.7 ± 0.4 (n= 10)]. Description (type material of H. macrocaulus). “Thickest fragments (stem or major branches) 6 mm wide at base and 200 mm long; branching profuse and irregular, originally all around stem” (Watson 2008: 173). Apparently, branching alternate at every third hydrotheca in the material examined. Branches originating just below cauline hydrothecae. Primary branches in turn giving rise to one or two secondary branches. Stem and branches divided into internodes by little marked, alternately arranged, oblique nodes (Fig. 6 F–H). Hydrothecae alternately arranged in two planes. Hydrothecae resting on adnate hydrophores (Fig. 6 F–H); ratio between adcauline length of hydrophore and diameter at diaphragm c. 1.0. Hydrotheca low and free, oblique, directed downwards (Fig. 6 F–H). Rim everted. Hydrotheca strongly widening distally, much more at adcauline side, forming a distinct concavity (Fig. 6 F). Adcauline hydrothecal side completely free and reaching next internode (Fig. 6 F–H). Adcauline hydrothecal side higher than abcauline one (Fig. 6 F–H). A distinct pseudodiaphragm present, much more marked towards adcauline side (Fig. 6 F). Gonothecae originating directly from lateral of hydrophore (i.e., neither pedicel nor apophysis present) (Fig. 6 G). Gonotheca inverted pear-shaped, strongly narrowing at base and broadly rounded at distal part (Fig. 6 I). Maximum diameter at distal fifth. Measurements (in µm). Hydrothecae: diameter at aperture 250–270, diameter at diaphragm 220–240, height abcauline wall 30–50, height adcauline wall 50–80. Hydrophore: adcauline length 220–250. Internodes: length 630–800, diameter 250–300. Gonothecae: height c. 1420, maximum diameter c. 800. Cnidome: heteronemes (only one type could be observed since observations were made on a microslide) 15–17.5 x 5 [19–24 x 7–9 according to Watson (2008)]. Description (PS 65 / 19). One branched, strongly polysiphonic stem c. 195 mm high. Stem giving rise to several strongly-developed, polysiphonic, primary branches which, in turn, form polysiphonic secondary ones. Polysiphonic branches giving rise to lower-order branches, most monosiphonic, but some slightly polysiphonic basally. Overall, up to five-order branching observed. Branches divided into internodes by alternately arranged, slightly oblique nodes. Hydrothecae resting on adnate hydrophores; ratio between adcauline length of hydrophore and diameter at diaphragm c. 1.3 (Fig. 7 A–C). Hydrotheca low, distinctly widening from diaphragm upwards (Fig. 7 A). Adcauline wall slightly larger than abcauline one (Fig. 7 A, B). Adcauline hydrothecal wall free to internode (Fig. 7 A). Hydrothecal aperture directed downwards. Sometimes a secondary hydrotheca present (Fig. 7 C). An oblique, usually well-marked pseudodiaphragm present (Fig. 7 A, C). Female gonothecae present, arising from hydrophore. Gonotheca flattened; terebratulid brachiopod-shaped, with one side shorter (Fig. 7 E, F), in lateral view, when immature, and fusiform when mature. In frontal view, gonotheca more or less triangular (Fig. 7 D, G). Measurements (in µm). Hydrothecae: diameter at aperture 245–250, diameter at diaphragm 190–220, height 35–50. Gonothecae: height 1300–1400, maximum diameter c. 500 (lateral view) and 700–780 (frontal view). Cnidome: innumerous isorhizas [range 17.5 –19.0 x 7.0–8.0, mean 18.3 ± 0.5 x 7.2 ± 0.3 (n= 10); ratio, range 2.4–2.7, mean 2.6 ± 0.1 (n= 10)], larger microbasic euryteles? [range 13.0–14.0 x 6.5–7.5, mean 13.5 ± 0.4 x 7.1 ± 0.4 (n= 5); ratio, range 1.8 –2.0, mean 1.9 ± 0.1 (n= 5)], smaller microbasic euryteles [range 6.0– 7.5 x 3.0– 3.5, mean 6.7 ± 0.4 x 3.4 ± 0.2 (n= 10); ratio, range 1.9–2.2, mean 2.0± 0.1 (n= 10)], and microbasic mastigophore (7.5–8 x 2 –2.5). Remarks. Stepanjants (1979) described two types of gonothecae, probably male and female. Putative male gonotheca oval, elongated with a distal, shallow groove. Female gonotheca pear-shaped, flattened, and with external acrocyst. In the material from PS 65 / 19 there are gonothecae with acrocyst where embryo is completing its development (Fig. 7 D) and others where embryo is little developed and still within the gonotheca with the surrounding acrocyst (Fig. 7 E–G). Apparently, shorter side deploys to allow embryo and acrocyst to exit (Fig. 7 D). Naumov & Stepanjants (1962) characterized this species by the structure of the hydrotheca. They indicated that the “obliquely cut aperture with turned out edges and the presence of two diaphragms in the hydrotheca separate the new species from all the known species of the genus Halecium ”. According to these authors, the species has stems “irregularly ramified in several planes”, “with primary and secondary branches polysiphonic”. The pseudodiaphragm is oblique. Interestingly, Naumov & Stepanjants (1962) also indicated that, “considering the type of ramification, the structure of the branches and the disposal of the hydrothecae, our species appear to be related to H. arboreum Allman ”. This clearly points to a colonial structure as that found in the material here assigned to H. incertus. Stepanjants (1979) also characterized the species by having very large colonies with thick and polysiphonic stems irregularly branched repeatedly in several planes. She also indicated that young colonies have a more ordered branching: primary branches alternately arranged, second-order ones in different planes. Millard (1977) described as Halecium dufresnae a new species that agrees in every detail with H. incertus and, in fact, Stepanjants (1979) already considered this species conspecific with H. incertus. Millard’s (1977) material also has thick fascicled stem (up to 245 mm high), branching and re-branching irregularly, but mainly in one plane. Although it has not been possible to re-describe the general appearance of the colony of H. macrocaulus from the material examined, according to Watson’s (2008) description it is clear that H. macrocaulus has robust, polysiphonic and much branched stems. In addition, although Watson (2008) indicated that forks arise from within a hydrotheca, in the material examined here I found only branches originating just below the cauline hydrothecae. Watson (2008: 173) also indicated the presence of a “septum (false diaphragm) of perisarc passing diagonally through hydrophore from near junction of diaphragm with abcauline wall to adcauline wall”. This “false diaphragm” clearly corresponds with a pseudodiaphragm as it has been unequivocally demonstrated by examining the holotype material of H. macrocaulus (cf. Fig. 6 F). Halecium macrocaulus is undistinguishable from H. incertus and it is considered here conspecific with Naumov & Stepanjants’ species. They agree in colony structure, with thick stems profusely and irregularly branched, shape and size of hydrotheca, presence of pseudodiaphragm, sessile hydrophores, and size of nematocysts. The single difference concerns the presence of acrocyst in H. incertus, not described for H. macrocaulus. However, this could be explained by the fact that the gonothecae described for H. macrocaulus are either male or female but immature. As it has been shown above, in H. incertus, it is possible to find in the same colony gonothecae with acrocyst, where an embryo is completing its development, together with others where an embryo is little developed and still within the gonotheca with the surrounding acrocyst. The shape of the gonotheca of H. macrocaulus [Fig. 6 I; see also Figure 9 B by Watson (2008: 174)] is identical to that I found in H. incertus from Bouvet (cf. Fig. 7 D, G). It seems clear, from the above-shown descriptions that H. incertus is characterised by having large (up to 300 mm high), thick, polysiphonic stems giving rise to also polysiphonic, lower-order branches in one or several planes. Consequently, I conclude that the material ascribed to H. incertus by Peña Cantero (2008, 2009, 2012) belongs to a different, described below, new species to science, Halecium pseudoincertus sp. nov. Ecology and distribution. Halecium incertus has been found at depths from 15 (Stepanjants 1979) to 693 m (Branch & Williams 1993), on rock (Stepanjants 1979; Branch & Williams 1993), and gravel and mud (Stepanjants 1979). Gonothecae in April (Millard 1977; Stepanjants 1979), November (Peña Cantero & Gili 2006), and from December to February (Stepanjants 1979). Halecium incertus seems to have an Antarctic –Kerguélen distribution (Peña Cantero & Gili 2006), having been found in both Antarctic and sub-Antarctic waters. In the latter, it is known from off Crozet (Millard 1977; Stepanjants 1979), Kerguélen (Stepanjants 1979) and the Marion and Prince Edward islands area (Branch & Williams 1993). In Antarctic waters, it is known from the Sodruzestva Sea (Naumov & Stepanjants 1962), off the Amery Ice Shelf (Stepanjants 1979), and off Mawson Coast (Watson 2008 as H. macrocaulus), in East Antarctica, and off Bouvet (Peña Cantero & Gili 2006).

Peña Cantero, Álvaro L. (2021): Additions to knowledge of the biodiversity of benthic hydroids (Cnidaria: Hydrozoa) in the Balleny Islands (Antarctica). Zootaxa 4966 (3): 321-336, DOI: https://doi.org/10.11646/zootaxa.4966.3.4

Filellum sp. (*) Filellum sp. Peña Cantero, 2009: 1747, fig. 3e. Remarks. Reported, from infertile material, off Sturge Island, at depths between 96 and 117 m, epibiont on Halecium incertus Naumov & Stepanjants, 1962 and Obelia bidentata Clark, 1875 (Peña Cantero 2009)., Published as part of Peña Cantero, Álvaro L., 2021, Additions to knowledge of the biodiversity of benthic hydroids (Cnidaria: Hydrozoa) in the Balleny Islands (Antarctica), pp. 321-336 in Zootaxa 4966 (3) on page 323, DOI: 10.11646/zootaxa.4966.3.4, http://zenodo.org/record/4736691, {"references":["Pena Cantero, A. L. (2009) Benthic hydroids (Cnidaria, Hydrozoa) from the Balleny Islands (Antarctica). Polar Biology, 32, 1743 - 1751. https: // doi. org / 10.1007 / s 00300 - 009 - 0673 - 7","Naumov, D. V. & Stepanjants, S. D. (1962) Hydroida (Thecaphora) collected by the Soviet Antarctic Expedition on the M / V Ob in antarctic and subantarctic waters. In: Biological results of the Soviet Antarctic Expedition, 1955 - 1958, 1. Issledovaniya Fauny Morei, 1 (9), 68 - 106.","Clark, S. F. (1875) Descriptions of new and rare species of hydroids from the New England coast. Transactions of the Connecticut Academy of Arts and Sciences, 3, 58 - 66."]}

Eudendrium sp. (*) Eudendrium sp. — Peña Cantero, 2009: 1745–1746, fig. 2a. Remarks. Peña Cantero (2009) found this hydroid off Young Island, at depths between 103 and 127 m, and with gonophores in March, indicating that the material was allied with Eudendrium cyathiferum Jäderholm, 1904, but that it was necessary to know the cnidome of Jäderholm's species to settle the issue., Published as part of Peña Cantero, Álvaro L., 2021, Additions to knowledge of the biodiversity of benthic hydroids (Cnidaria: Hydrozoa) in the Balleny Islands (Antarctica), pp. 321-336 in Zootaxa 4966 (3) on page 323, DOI: 10.11646/zootaxa.4966.3.4, http://zenodo.org/record/4736691, {"references":["Pena Cantero, A. L. (2009) Benthic hydroids (Cnidaria, Hydrozoa) from the Balleny Islands (Antarctica). Polar Biology, 32, 1743 - 1751. https: // doi. org / 10.1007 / s 00300 - 009 - 0673 - 7","Jaderholm, E. (1904) Mitteilungen ueber einige von der Schwedischen Antarctic Expedition 1901 - 1903 eingesammelte Hydroiden. Archives de Zoologie Experimentale et Generale, Series 4, 3 (Notes et revue 1), 1 - 14."]}

Filellum antarcticum (Hartlaub, 1904) (Fig. 1A–C) Material examined. E203, several hydrothecae and two coppiniae, on Stegella lobata (Vanhöffen, 1910) (NIWA 128467). Remarks. The presence of coppinia in the present material allows identification with confidence. The nestshaped coppinia consists of closely packed gonothecae (Fig. 1A) surrounded by a fence of distally open defensive tubes arching over them. The gonothecae are deprived of distal neck (Fig. 1B). Some of them, however, with distal part slightly raised (Fig. 1C), but never forming a distally everted neck as found in the other known Antarctic species of the genus, Filellum magnificum Peña Cantero, Svoboda & Vervoort, 2004. The gonotheca is roughly 260 µm high, 130 µm in maximum diameter, and 65–70 µm in diameter at aperture. The shape and size of the hydrothecae in the present material also match Hartlaub’s species, with a hydrothecal diameter of 100–120 µm. Ecology and distribution. The material, which represents the first record for the area, was collected at a depth of 187 m off Sturge Island, epibiotic on S. lobata. Coppiniae in January.

Campanularia sp. (Fig. 4A–D) Campanularia tincta.— Vanhöffen, 1910: 297–298, fig. 17d, e (only material from Kerguelen). Campanularia sp. — Millard, 1977: 18–20, fig. 5F. Material examined. PROTEKER 3: Ile Suhn, several hydrothecae on algae, C. pusilla and tubulariid stem (MNHN IK –2012–10430). Description. Stolonal hydrorhiza giving rise to erect, slightly sinuous, smooth pedicels up to 2200 µm long and provided with a single distal hydrotheca. Hydrotheca elongated (Fig. 4A), bell-shaped, 930–940 µm high, resting on a basal spherule, 50 µm high and 80 µm wide, clearly thinner than pedicel and basal chamber (Fig. 4D); basal chamber 60 µm high. Apparently without diaphragm. Distinct inflexion point at distal part of basal chamber (Fig. 4A, D); hydrothecal diameter markedly increasing just above basal chamber, smoothly up to the middle and roughly constant afterwards, distinctly increasing again at base of cusps (Fig. 4A, C). Hydrothecal aperture perfectly circular, 370 µm in diameter; rim provided with 12 sharp cusps (height 60 µm, distance between cusps 80–90 µm) (Fig. 4A, C), very slightly directed inwards and separated by deep embayments. Hydrotheca with fine longitudinal streaks running downwards from the cusps (Fig. 4A, C). Frequently with hydrothecal renovations (Fig. 4C) (up to third-order hydrothecae observed). Microbasic mastigophores, banana-shaped, 18.1±1.0 x 4.0±0.1 µm (n= 10), range 16.5–19.5 x 4.0–4.3 µm. Remarks. In the sample studied, there are also distinctly larger and wider hydrothecae (Fig. 4B). They are bellshaped, 1030–1100 µm high and 430 µm in diameter at the aperture, resting on a basal spherule, 70 µm high and 110 µm wide, clearly much thinner than the basal chamber and the pedicel; basal chamber 80 µm high. In general, these hydrothecae lack the distinctive inflexion point above the basal chamber found in the others, the diameter gradually increasing from the basal part of the basal chamber to the distal third of the hydrotheca. They also lack the characteristic enlargement at the base of the cusps. The hydrotheca is provided with 14 long, thin cusps (height 80 µm, distance between cusps 100 µm). The microbasic mastigophores, also banana-shaped, are slightly smaller 16.0±0.7 x 4.0±0.3 µm (n= 10), range 15–17 x 3.5–4 µm. It could not be determined whether both types of hydrothecae belong to the same species. Present material appears to be conspecific with the material described as Campanularia sp. by Millard (1977) from the nearby Crozet Islands. In her material, the hydrotheca is also deep, 600–900 µm high, but slightly thinner (250–330 µm in diameter at the rim), with parallel sides and a basal spherule of smaller diameter than the pedicel. Millard reported eight to ten thin, bluntly rounded cusps, but did not mention any increase in hydrothecal diameter at the base of the cusps. Allman (1876; 1879) described a new species, Campanularia cylindrica, from Kerguelen. The material was provided with gonothecae “cylindrical above, with a flat summit, tapering below towards the very short peduncle, which springs from the creeping stolon.” Allman stated that “in the absence of any fuller knowledge of its gonosome, this species … is only provisionally referred to the genus Campanularia ”. According to Vanhöffen (1910), Allman’s species has gonothecae similar to those of Clytia. The material studied here agrees with Allman’s in the elongated shape of the hydrotheca, as well as in the number of hydrothecal cusps, but the basal part of the hydrotheca is clearly different. In conclusion, the present material with elongated hydrothecae is almost certainly conspecific with Millard’s material and could be conspecific with Allman’s species; the material with larger and wider hydrothecae is otherwise similar to that reported from Kerguelen, as C. tincta Hincks, 1861, by Vanhöffen (1910: 297, fig. 17d–e). However, the absence of gonothecae here, as was also the case in Millard’s and Vanhöffen’s material, precludes the identification to species level. Ecology and distribution. Campanularia sp. was collected at a depth of 14 m off Suhm Island, epibiotic on algae, C. pusilla and tubulariid stem., Published as part of Peña Cantero, Álvaro L., 2022, On a few benthic hydroids (Cnidaria, Hydrozoa) from the Kerguelen Islands (southern Indian Ocean), including the description of a new species, pp. 274-286 in Zootaxa 5165 (2) on pages 281-282, DOI: 10.11646/zootaxa.5165.2.7, http://zenodo.org/record/6831887, {"references":["Vanhoffen, E. (1910) Die Hydroiden der Deutschen Sudpolar-Expedition 1901 - 1903. Deutsche Sudpolar-Expedition 1901 - 1903, 11 (Zoology 3), 269 - 340.","Millard, N. A. H. (1977) Hydroids from the Kerguelen and Crozet shelves, collected by the cruise MD. 03 of the Marion-Dufresne. Annals of the South African Museum, 73 (1), 1 - 47.","Allman, G. J. (1876) Descriptions of some new species of Hydroida from Kerguelen's Island. Annals and Magazine of Natural History, Series 4, 17, 113 - 115. https: // doi. org / 10.1080 / 00222937608681913","Allman, G. J. (1879) Hydroida. In: An account of the petrological, botanical, and zoological collections made in Kerguelen's Land and Rodriguez during the transit of Venus Expeditions, carried out by order of Her Majesty's government in the years 1871 - 1875. Philosophical Transactions of the Royal Society of London, 168 (Extra Volume), 282 - 285.","Hincks, T. (1861) On new Australian Hydrozoa. The Annals and Magazine of Natural History, 7 (3), 279 - 281, pls. 12 - 13."]}

Oswaldella sp. 1 (*) Oswaldella sp. 1 — Peña Cantero, 2009: 1749, fig. 3b. Remarks. Peña Cantero (2009) considered material of Oswaldella he studied conspecific with the material described as Oswaldella sp. 1 by Peña Cantero & Vervoort (2004). The material was collected off Buckle Island, at a depth of 85 m.

Zygophylax pseudoabietinella sp. nov. (Figs 1 G–H, 7D–E, 9) urn:lsid:zoobank.org:act: 93001359-55B9-4478-8297-A435BE8AA730 Material examined. MUSORSTOM 4 Stn CP 155, 18°52.8’S– 163°19.5’E (N of New Calendonia), 500–570 m, 15.09.1985: seven stems up to 25 mm high, one with coppinia (25-mm-high stem with coppinia holotype, MNHN-IK-2019-2048; remaining material paratype, MNHN-IK-2019-2049). Description. Stems up to 25 mm high (Fig. 1G), polysiphonic for most of their extension. Stem giving rise to hydrocladia alternately in one plane, but with hydrocladia grouped in sub-opposite pairs (Fig. 1G) and with two hydrothecae between successive pairs. Hydrocladia basally polysiphonic, except those from distal monosiphonic part of stems. Some basal hydrocladia much developed (Fig. 1G), becoming polysiphonic branches or lower-order stems and giving rise in turn to hydrocladia (up to fourth-order hydrocladia present).Angle between hydrocladia and branches or stems 70°. Branches and hydrocladia in a slight zigzag pattern. Stems, branches and hydrocladia giving rise to hydrothecae alternately arranged almost in one plane (Figs 1G, 7 D–E, 9A–B). Hydrotheca roughly cylindrical (Figs 7 D–E), diameter more or less constant, sigmoid. Hydrotheca bent outwards and then inwards at distal part. Adcauline wall convex for its basal two thirds and concave at its distal third. Abcauline wall slightly concave at basal half and slightly convex at distal half. Walls faintly striated transversally. Hydrothecal aperture circular, slightly oblique to hydrothecal long axis. Some hydrothecae with a closing apparatus consisting of a circular flap (Figs 7E, 9 D–E). Hydrothecal diaphragm consisting of a strongly developed ring of perisarc, slightly oblique (abcauline side somewhat higher); diaphragm sometimes duplicated or even triplicated (Fig. 9F) Hydrothecal pedicel indistinguishable from apophysis (Figs 7 D–E, 9A–G). Typically two nematothecae on hydrothecal apophyses, one on each side (Fig. 9G). Sometimes only one present and occasionally both absent, particularly in the youngest distal hydrothecae (Fig. 7E). For hydrocladial apophyses, pair of nematothecae placed beyond first hydrothecal apophysis, which is deprived of nematothecae (Figs 7D, 9A). Nematothecae also present on accessory tubes, though not very abundant. Nematotheca cylindrical, short, with a wide distal aperture (Fig. 9G). One coppinia, 3 mm in diameter, present on one stem, on one side (Fig. 1 G–H). With a few branched tubes arising between gonothecae (Fig. 1H). Abietinella -like gonotheca, distal part forming a hood-like structure, provided with a lateral aperture (Figs 1H, 9H). Measurements (in µm). Hydrothecae: length of abcauline wall 420–460, length of adcauline wall 400–420, diameter at aperture 130–140, diameter at diaphragm 80–100, maximum diameter 120, length of pedicel 140–200. Nematothecae: height 60–75, diameter at aperture 25–30, maximum diameter 30–35. Gonothecae: height of distal hooded part 300, aperture 150. Remarks. The circular flap found at the distal part of several hydrothecae seems to have no fixed insertion (it was observed on the adcauline side in some hydrothecae, but on the abcauline side in others). Among the known species of Zygophylax, the present species is morphologically similar to Z. kakaiba Campos, Marques, Puce & Pérez, 2016 in colony structure, but their trophosomes differ in the shape of the hydrothecae. In Z. kakaiba the hydrotheca is swollen with the adcauline wall convex except for the most distal part, whereas in Z. pseudoabietinella sp. nov. the diameter of the hydrotheca is more or less constant and the adcauline wall is slightly convex for its basal two thirds and slightly concave at its distal third. Furthermore, whereas the aperture is parallel to the longitudinal axis of the hydrotheca in Z. kakaiba, it is almost perpendicular to that axis in Z. pseudoabietinella sp. nov. The hydrotheca of Z. kakaiba is also smaller (e.g. 290–330 µm in length of adcauline wall). The reproductive structure is unknown for Z. kakaiba. Zygophylax pseudoabietinella sp. nov. is also morphologically similar to Abietinella operculata (Jäderholm, 1903), but Jäderholm’s species has distinctly larger and more robust hydrothecae (e.g. 715–748 µm in height and 215–241 µm in diameter at aperture in Peña Cantero et al. 2004) and nematothecae (e.g. 163–280 µm in height and 52–65 µm in diameter at aperture in Peña Cantero et al. 2004). Furthermore, the hydrotheca is swollen in A. operculata. Both species also share the presence of a circular flap as a closing apparatus in some hydrothecae, but whereas it is inserted on the adcauline side of the hydrothecal aperture in A. operculata, it has no fixed insertion in Z. pseudoabietinella sp. nov. Etymology. The specific name pseudoabietinella refers to the fact that in this species the shape of the hydrotheca resembles that of Abietinella operculata (Jäderholm, 1903)., Published as part of Peña Cantero, Álvaro L., 2020, On six new species of Zygophylax Quelch, 1885 (Cnidaria, Hydrozoa Zygophylacidae) from the New Calendonian region, pp. 389-404 in Zootaxa 4822 (3) on pages 400-403, DOI: 10.11646/zootaxa.4822.3.4, http://zenodo.org/record/4401711, {"references":["Campos, F. F., Marques, A. C., Puce, S. & Perez, C. D. (2016) Zygophylax kakaiba, a new species of hydroid (Cnidaria: Hydrozoa: Zygophylacidae) from the Philippine Islands. Zootaxa, 4088 (3), 438 - 444. https: // doi. org / 10.11646 / zootaxa. 4088.3.9","Jaderholm, E. (1903) Aussereuropaischen Hydroiden im schwedischen Reichsmuseum. Arkiv for Zoologi, 1, 259 - 312.","Pena Cantero, A. L., Svoboda, A. & Vervoort, W. (2004) Antarctic hydroids (Cnidaria: Hydrozoa) of the families Campanulinidae, Lafoeidae and Campanulariidae from recent Antarctic expeditions with R. V. Polarstern, with the description of a new species. Journal of Natural History, 38, 2269 - 2303. https: // doi. org / 10.1080 / 00222930310001647361"]}

Zygophylax medeae sp. nov. (Figs 1E, 6, 7A) urn:lsid:zoobank.org:act: 903897FE-7295-4144-8510-EADE9EB347FA Material examined. BIOGEOCAL Stn CP 205, 22°40.61’– 22°41.07’S, 166°28.01’– 166°27.63’E (off SW of New Caledonia), 1350–1380 m, 08.04.1987: 27-mm-high stem, with gonothecae (all in slide) (Holotype, MNHN-IK-2019- 2045). Description. Stem polysiphonic, 27 mm high, with only a few hydrocladia and three hydrothecae left (Fig. 1E). Hydrocladial apophyses large (Figs 6A, D, 7A), much larger than hydrothecal apophyses, markedly separated from hydrocladia. Hydrocladia with a basal oblique ring (Fig. 6A, D). Basal part of first internode slightly swollen (Fig. 6A, D). Hydrocladia monosiphonic (Fig. 1E), divided into very long internodes; hydrothecae relatively separated (Fig. 1E). Angle between apophyses and hydrocladia 80°. Hydrothecal apophysis short, apparently without nematothecae. Distinct separation between hydrothecal apophysis and hydrothecal pedicel. Hydrothecae tubiform (Figs 6 B–D, 7A), more or less symmetrical, roughly straight, though slightly convex at adcauline side and slightly concave at abcauline side. Pedicel long (Figs 6 C–D, 7A), separated from hydrotheca by a slightly oblique diaphragm, marked by a thin ring of perisarc (Figs 6 C–D, 7A). Aperture circular, rim even with up to six renovations (Fig. 6C). Diameter of hydrothecae smoothly increasing to aperture. Only a few nematothecae on accessory tubes present. Nematothecae elongate, cylindrical (Fig. 6 E–F). Three gonothecae present (Fig. 1E). Gonotheca outline fusiform, but distal part with two opposing arms, each with a distal wide aperture (Figs 1E, 6F). Measurements (in µm). Hydrothecae: length of abcauline wall 650–680, length adcauline wall 630–650, diameter at aperture 160–190, diameter at diaphragm 100, basal diameter 80–90, length of pedicel 480–500. Nematothecae: height 300–320, diameter at aperture 25, maximum diameter 40–50. Gonothecae: height 850–870, diameter at aperture c. 120, maximum diameter 350–380. Remarks. The scarcity of material prevents me from determining the arrangement of the hydrothecae and the number of nematothecae on apophyses. Zygophylax medeae sp. nov. is similar to Z. recta Jarvis, 1922 by the shape of the hydrotheca, although they are clearly distinguishable by the length of the pedicel, markedly much shorter in Z. recta. They also differ in the size of the hydrothecae, smaller in Z. recta (e.g. 150 µm in diameter at aperture), and nematothecae, shorter in Jarvis’s species (70–100 µm in height). Etymology. The specific name medeae is a dedication to my daughter Medea Peña Sancho., Published as part of Peña Cantero, Álvaro L., 2020, On six new species of Zygophylax Quelch, 1885 (Cnidaria, Hydrozoa Zygophylacidae) from the New Calendonian region, pp. 389-404 in Zootaxa 4822 (3) on pages 397-400, DOI: 10.11646/zootaxa.4822.3.4, http://zenodo.org/record/4401711, {"references":["Jarvis, F. E. (1922) The hydroids from the Chagos, Seychelles and other islands and from the coasts of British East Africa and Zanzibar. In Reports of the Percy Sladen Trust Expedition to the Indian Ocean in 1905, under the leadership of Mr J. Stanley Gardiner, M. A. Transactions of the Linnean Society, London, Zoology, Series 2, 18 (1), 331 - 360, pls. 24 - 26. https: // doi. org / 10.1111 / j. 1096 - 3642.1922. tb 00553. x"]}

Zygophylax laertesi sp. nov. (Figs 1D, 3 F–H, 5) urn:lsid:zoobank.org:act: F12154FC-7F72-4255-B8C4-0202B01B6413 Material examined. MUSORSTOM 4 Stn CP 216, 22°59.5’S– 167°22.0’E (off Koutoumo Island, New Caledonia region), 490–515 m, 29.09.1985: one stem 40 mm high, with coppinia (Holotype, MNHN-IK-2019-2044). Description. Stem 40 mm high (Fig. 1D), stiff, strongly and almost completely polysiphonic. Stem with alternately arranged apophyses giving rise to hydrothecae and hydrocladia. Branching alternate, in one plane, but with hydrocladia grouped in sub-opposite pairs (Fig. 1D, 3F, 5A) and with two hydrothecae between successive pairs. A basal pair of hydrocladia (and another higher) much developed (Fig. 1D), becoming second-order stems or branches and giving rise in turn to hydrocladia. Hydrocladia polysiphonic for most of their extension, except for the youngest ones. Faint separation between hydrocladial apophyses and hydrocladia (Fig. 3F). Angle between stem or branches and hydrocladia 70° (Fig. 1D). Hydrocladia roughly straight (Fig. 1D). Hydrothecae alternately arranged in one plane (Figs 3G, 5C), resting on short apophyses (Figs 3G, 5C). Separation between apophysis and hydrothecal pedicel usually marked only by a strong constriction of perisarc (Figs 3 F–G, 5A–D, F–G), very sharp on adcauline side (occasionally a node present). Hydrotheca tubiform (Figs 3 F–G, 5), curved, sigmoid, tapering at base. Hydrotheca bent outwards first, then inwards (Figs 3G, 5 C–D). Adcauline wall convex at basal half and concave at distal half; conversely, abcauline wall convex at distal half and slightly concave at basal half. Aperture circular, rim even but flared, with up to five renovations. Diameter of hydrothecae roughly constant at distal half, but hydrotheca slightly swollen at basal half. Hydrothecal wall with faint transverse wrinkles. A marked internal adcauline cusp present (Figs 3G, 5 C–D, F). Hydrothecal diaphragm marked by a strong, oblique ring of perisarc; diaphragm higher at abcauline side (Figs 3G, 5D, F–G). An internal vertical keel present on abcauline hydrothecal wall above diaphragm (Figs 3G, 5 C–D, F–G). A dish-shaped operculum present in some hydrothecae (Fig. 3D, F). Two nematothecae resting on hydrothecal and hydrocladial apophyses, one on each side (Fig. 3G). Nematothecae on hydrocladial apophyses beyond first hydrothecal apophysis, which is provided with nematothecae (Fig. 3F, 5B). Striking abundance of nematothecae on accessory tubes (Fig. 5 A–B, H), longer and thinner than those on hydrothecal apophyses. Nematothecae elongate, frequently with extra segments (up to five observed) (Fig. 3F). Coppinia rounded (Fig. 1D), with an envelope of forked tubes (Fig. 1D) covering independent gonothecae. Gonotheca with inverted pear-shaped outline, with a narrow basal part and a much wider distal one, which form two very short arms with a distal aperture (Fig. 3H). Measurements (in µm). Hydrothecae: length of abcauline wall 430–460, length of adcauline wall 380–390, diameter at aperture 75–80, diameter at diaphragm 50–60, length of pedicel 80–100. Nematothecae on apophyses: height 90–100, diameter at aperture 15, maximum diameter 25–30. Nematothecae on accessory tubes: height 170– 250, diameter at aperture 8–15, maximum diameter 20. Gonothecae: height 500–550, diameter at aperture 80–100, maximum diameter 400–500. Remarks. Zygophylax laertesi sp. nov. is easily recognizable amongst the known species of the genus by the shape of the hydrotheca, the internal adcauline cusp and the abcauline vertical keel above the diaphragm. Zygophylax laertesi sp. nov. resembles no other described species. Etymology. The specific name laertesi is a dedication to my son Laertes Peña Sancho., Published as part of Peña Cantero, Álvaro L., 2020, On six new species of Zygophylax Quelch, 1885 (Cnidaria, Hydrozoa Zygophylacidae) from the New Calendonian region, pp. 389-404 in Zootaxa 4822 (3) on pages 394-397, DOI: 10.11646/zootaxa.4822.3.4, http://zenodo.org/record/4401711

Zygophylax dispersa sp. nov. (Figs 1 A–B, 2, 3A–B) urn:lsid:zoobank.org:act: 37FF8BBE-19DC-4907-AA4A-D88087ADE03A Material examined. BIOGEOCAL Stn CP 297, 20°38.64’– 20°38.67’S, 167°10.77’– 167°11.07’E (off Lifou, Loyalty Islands, New Caledonian region), 1230–1240 m, 28.04.1987: one stem 45 mm high, with two coppiniae (Holotype, MNHN-IK-2019-2042). Description. Erect, stiff stem 45 mm high (Fig. 1A), almost completely polysiphonic, slightly geniculate (Fig. 2A), yellowish-coloured. Branching alternate in one plane, though hydrocladia grouped in sub-opposite pairs; two hydrothecae between successive pairs. Branches or lower-order stems formed by much-developed hydrocladia that become strongly polysiphonic and that give rise in turn to new hydrocladia, which may also undergo further development and become lower-order branches (up to third-order branches present). Angle between stem or branches and hydrocladia 60–70° (Fig. 1A). Even though branching is typically alternate, some of the strongly polysiphonic primary branches frontally directed, forming two planes with a very open angle. Polysiphony even present in the hydrocladia, which are monosiphonic only distally. Hydrocladia straight (Fig. 2B), resting on apophyses, with distinct perisarc constriction between them (Fig. 2A). Corresponding cauline hydrotheca on apophysis resting on hydrocladial apophysis (Fig. 2C). Hydrocladial apophyses with two nematothecae, one on each side, placed beyond hydrothecal apophysis, which is deprived of nematothecae (Figs 2A, C, 3A). Hydrothecae on short apophyses (Figs 2B, D–E, 3B), with distinct separation between hydrothecal pedicel and apophysis, marked by a node and a distinct reduction in diameter. Hydrothecae alternately arranged in one plane (Fig. 2B). Relatively large distance between hydrothecae (Figs 1A, 2 A–B). Hydrotheca cylindrical, diameter roughly constant along distal two-thirds, smoothly decreasing towards pedicel (Figs 2 A–E, 3A–B). Abcauline wall roughly straight; adcauline one slightly convex at basal half, but straight at distal half (Figs 2 D–E, 3B). Aperture circular. Rim even, slightly everted, with up to three, relatively long, renovations. Pedicel short, separated from hydrotheca by a distinct annular diaphragm (Figs 2 D–E, 3A–B). Pedicel abcauline side straight or slightly concave, adcauline one slightly convex (Figs 2B, E, 3B). Sometimes, a short ring (likely related to regeneration) between apophysis and hydrothecal pedicel (Fig. 2D), giving the pedicel a ringed appearance. Two nematothecae on apophyses (Fig. 2A), one on each side, resting on short pedicel (Fig. 2F). Nematothecae low, roughly cylindrical, with a large distal circular aperture (Fig. 2F); sometimes with one distal extra segment. Coppinia fusiform (Fig. 1 A–B), composed of closely packed gonothecae (Fig. 1B, 2 G–H). Gonotheca bottleshaped, widening from base to top of contiguous portion and proceeding with a slenderer hood-shaped distal part with lateral aperture (Fig. 2H). Without defensive tubes (Fig. 1 A–B). Measurements (in µm). Hydrothecae: height 250–350, diameter at aperture 85–100, diameter at diaphragm 60– 70, length of pedicel 50–70. Nematothecae: height 45–50, diameter at aperture 25–35, maximum diameter 30–40. Gonothecae: height 550–560 (distal part 150–180), maximum diameter 200–300, aperture 70 x 100. Remarks. Zygophylax dispersa sp. nov. is morphologically close to Z. crozetensis Millard, 1977 in the general shape of hydrothecae and nematothecae, but Millard’s species has distinctly larger hydrothecae (e.g. 160–200 µm in diameter at hydrothecal aperture) and nematothecae (e.g. height 90–190, diameter at aperture 50–80). They also differ in the structure of the coppinia (that of Z. crozetensis having irregularly branching structures arising among the gonothecae and provided with nematothecae and rarely hydrothecae) and the shape of the gonothecae (those in Millard’s species have a pointed, sometimes curved, horn). In addition, in Z. crozetensis, hydrothecae are more packed together and hydrocladia are divided into internodes, each with one or two hydrothecae. Finally, the hydrothecal diaphragm is oblique in Z. crozetensis, but transverse in our material. By the shape of the hydrotheca, Z. dispersa sp. nov. is also similar to Z. sagamiensis Hirohito, 1983, but the two species differ is several features. The colony of Z. dispersa sp. nov. is stiff and almost completely polysiphonic, while that of Z. sagamiensis has hydrocladia polysiphonic only on their basal part (occasionally further on their distal part). Whereas Hirohito’s species is characterised by usually having one to five internodes between hydrothecal pedicel and apophysis, in Z. dispersa sp. nov. only a short ring between apophysis and pedicel has been occasionally observed (probably due to regeneration). In addition, the hydrotheca in Z. sagamiensis is much larger (e.g. 450–500 µm in length). Finally, the shape of the gonotheca is completely different, because the gonothecae have a long sharp distal projection in Hirohito’s species. Etymology. The specific name dispersa refers to the fact that the hydrothecae are separated by a relatively large distance., Published as part of Peña Cantero, Álvaro L., 2020, On six new species of Zygophylax Quelch, 1885 (Cnidaria, Hydrozoa Zygophylacidae) from the New Calendonian region, pp. 389-404 in Zootaxa 4822 (3) on pages 389-390, DOI: 10.11646/zootaxa.4822.3.4, http://zenodo.org/record/4401711, {"references":["Millard, N. A. H. (1977) Hydroids from the Kerguelen and Crozet shelves, collected by the cruise MD. 03 of the Marion-Dufresne. Annals of the South African Museum, 73, 1 - 47.","Hirohito, Emperor of Japan (1983) Hydroids from Izu Oshima and Niijima. Publications Biological Laboratory, Imperial Household, Tokyo, 1983 (6), 1 - 83."]}

Zygophylax encarnae sp. nov. (Figs 1C, 3 C–E, 4) urn:lsid:zoobank.org:act: 18C48841-985C-453B-BF3E-1C95A70EFB7E Material examined. BIOGEOCAL Stn CP 265, 21°04.09’– 21°04.74’S, 167°00.40’– 166°59.71’E (off Lifou, Loyalty Islands, New Caledonian region), 1760–1870 m, 18.04.1987: one stem 40 mm high, with gonothecae (Holotype, MNHN-IK-2019-2043). Description. One stem 40 mm high, broken into three fragments. Stem strongly, almost completely, polysiphonic (Fig. 1C). Stem with alternately arranged apophyses giving rise to hydrothecae and hydrocladia. Branching alternate, in one plane, but with hydrocladia grouped in sub-opposite pairs (Fig. 1C) and with two hydrothecae between successive pairs. All hydrocladia almost completely polysiphonic. A few basal hydrocladia much developed, becoming branches or lower-order stems and giving rise in turn to hydrocladia (Fig. 1C). Angle between stem or branches and hydrocladia 70–80° (Fig. 1C). Hydrocladia straight, relatively very long, with up to 35 hydrothecae (Fig. 1C), resting on hydrocladial apophyses (Fig. 4A). More or less distinct separation between hydrocladia and apophyses. Hydrocladial apophyses with two nematothecae, one on each side, beyond first hydrothecal apophysis, which is deprived of nematothecae (Figs 3C, 4B). Hydrothecae almost with unilateral arrangement, alternate, distally directed, but curved outwards (Figs 3D, 4 C–D). Hydrothecae resting on short apophyses alternately arranged in two planes making an acute angle (Figs 3D, 4 C–D). Hydrotheca with a short, cone-shaped pedicel (Figs 3 C–D, 4E–F), distinctly separated from apophysis by a node and a distinct change in diameter (Figs 3 C–D, 4E–F). Hydrotheca elongate (Figs 3 C–D, 4A, C–E), relatively long and thin, curved outwards, sigmoid.Adcauline wall convex at basal half and concave at distal half; abcauline side convex, sometimes slightly concave basally (Figs 3 C–D, 4A, C–E). Maximum diameter by the middle; diameter decreasing distally and basally (minimum diameter at pedicel origin). Aperture circular, directed outwards and upwards. Rim even, with up to seven short renovations. Hydrothecal diaphragm consisting of a ring of perisarc, slightly oblique; abcauline side somewhat higher (Fig. 4E). One nematotheca on each hydrothecal apophysis, outside the space delimited by the hydrothecae. Nematotheca elongate (Fig. 4G), club-shaped, maximum diameter at distal third, strongly decreasing to distal end; aperture relatively tiny (Fig. 4G). Sometimes nematotheca consisting of a series of marked segments (up to three), likely due to regeneration. Nematothecae frequently with an extra distal segment. Small coppinia present, consisting of a few isolated gonothecae originating at basal part of tubes (Fig. 4H). Gonotheca ovoid, but with two very short distal arms, each with one aperture (Figs 3E, 4H). Measurements (in µm). Hydrothecae: length of abcauline wall 500–700, length of adcauline wall 520–610, diameter at aperture 110–130, diameter at diaphragm 80–90, length of pedicel 100–130, maximum diameter 130–140. Nematothecae: height 150–250, diameter at aperture 8–10, maximum diameter 45–60. Gonothecae: height 1000, maximum diameter 560, diameter at aperture 160. Remarks. Zygophylax encarnae sp. nov. is easily distinguishable from the remaining species of the genus by the almost completely unilateral arrangement of the hydrothecae and their peculiar shape. With the proper orientation, some hydrothecae somewhat resemble those of Z. adhaerens Fraser, 1938, but they are actually quite different as in Fraser’s species the hydrothecae are regularly curved, not sigmoid as in Z. encarnae sp. nov., and alternately arranged in one plane (hydrothecae are almost unilateral in Z. encarnae sp. nov.). In addition, there is no distinction between hydrothecal apophyses and the hydrothecal pedicel in Z. adhaerens. Etymology. The species name encarnae is a dedication to my wife Encarna Sancho Aguilar., Published as part of Peña Cantero, Álvaro L., 2020, On six new species of Zygophylax Quelch, 1885 (Cnidaria, Hydrozoa Zygophylacidae) from the New Calendonian region, pp. 389-404 in Zootaxa 4822 (3) on page 394, DOI: 10.11646/zootaxa.4822.3.4, http://zenodo.org/record/4401711, {"references":["Fraser, C. M. (1938) Hydroids of the 1934 Allan Hancock Pacific Expedition. Allan Hancock Pacific Expeditions, 4 (1), 1 - 105, pls. 1 - 15."]}

Zygophylax niobae sp. nov. (Figs 1F, 7 B–C, 8) urn:lsid:zoobank.org:act: 353672F0-A2D0-4061-967A-081E319B74DC Material examined. BIOCAL 1 Stn DW 36, 23°08.64’– 23°08.90’S, 167°10.99’– 167°11.29’E (S of New Caledonia), 650–680 m, 29.08.1985: a few stems up to 20 mm high (Holotype, MNHN-IK-2019-2046; paratype, MNHN-IK-2019-2047). Description. Stems up to 20 mm high, slightly polysiphonic except for their most distal part (Fig. 1F). Stems and branches in a distinct zigzag pattern (Figs 1F, 7B, 8A). Hydrocladia monosiphonic or slightly polysiphonic basally (Fig. 1F). First-order branching alternate, in one plane, but with hydrocladia grouped in sub-opposite pairs (Figs 1F, 7B, 8A) and with two hydrothecae between successive pairs. Some hydrocladia becoming branches or lower-order stems and usually giving rise to a single hydrocladium, usually directed frontwards, at its first internode (Fig. 1F). However, some primary branches more developed, with extra secondary hydrocladia (Fig. 1F). Branching frequent (up to fourth-order branches present). Separation between apophyses and hydrocladia usually marked only by a strong constriction of perisarc (Figs 7B, 8 A–C). Angle between apophyses and hydrocladia 45–50°. Hydrothecae on one side of stem, in two planes (Fig. 8D); angle more acute distally. Hydrotheca campanulate (Figs 7 B–C, 8), bent adcaudally. Abcauline wall convex, adcauline one concave. Aperture circular, rim flared, usually with a few renovations. Pedicel short, cone-shaped (Figs 7 B–C, 8), separated from hydrotheca by a thin ring of perisarc. Typically, with a relatively long intermediate internode between apophysis and pedicel (Figs 7 B–C, 8); intermediate internode slightly swollen at distal end (Figs 7 B–C, 8). Hydrothecal apophyses and intermediate internode separated by a strong constriction of perisarc (Figs. 7C). Nematothecae not observed (they might be absent). Gonothecae absent. Measurements (in µm). Hydrothecae: length of adcauline wall 200–240, length of abcauline wall 250–350, diameter at aperture 100–120, diameter at diaphragm 50, length of pedicel 60–80, length of intermediate internode 160–250. Remarks. Zygophylax niobae sp. nov. is similar to Z. bifurcata Billard, 1942 in the general shape of the hydrotheca. However, in Z. bifurcata the hydrotheca, more or less symmetrical, is straight, whereas in Z. niobae sp. nov. it is markedly bent. The hydrothecae are also distinctly larger in Z. bifurcata (155–185 µm in diameter at aperture, 320–365 µm in length from diaphragm to rim). In Z. bifurcata, according to Ramil & Vervoort (1992), who re-described the species, the pedicel is long, with wrinkled to indistinctly ringed portions. In Z. niobae sp. nov. the cone-shaped pedicel is short, and there is a long intermediate internode between hydrothecal apophysis and pedicel; occasionally, instead of a long intermediate internode there is a series of shorter ones, likely as a result of regeneration. The pedicel in Z. bifurcata is much longer (460–570 µm) than in Z. niobae sp. nov. (60–80 µm), even including the length of the intermediate internode (160–250 µm). Etymology. The specific name niobae is a dedication to my daughter Níobe Peña Sancho., Published as part of Peña Cantero, Álvaro L., 2020, On six new species of Zygophylax Quelch, 1885 (Cnidaria, Hydrozoa Zygophylacidae) from the New Calendonian region, pp. 389-404 in Zootaxa 4822 (3) on page 400, DOI: 10.11646/zootaxa.4822.3.4, http://zenodo.org/record/4401711, {"references":["Billard, A. (1942) Note sur une nouvelle espece et une nouvelle variete de Zygophylax (hydroides). Bulletin de la Societe zoologique de France, 67, 34 - 36.","Ramil, F. & Vervoort, W. (1992) Report on the Hydroida collected by the \" BALGIM \" expedition in and around the Strait of Gibraltar. Zoologische Verhandelingen, 277, 1 - 262."]}

Acryptolaria longitheca (Allman, 1877) (Figs 2C, 4 B–C, 5F, 7D) Cryptolaria longitheca Allman, 1877: 18–20, pl. 13, figs 4–5. Acryptolaria longitheca— Peña Cantero et al., 2007: 252 –254, figs 9, 16A, 18B; Peña Cantero & Vervoort, 2010: 297–299, figs 15, 30, 32A; Calder, 2019: 26 –27, figs 6a, b, 7a. Material examined. Eltanin : 27/1974, one stem, 31 mm high, and several fragments. Description. Stem polysiphonic. Hydrothecae alternate, more or less in one plane, roughly with straight arrangement. Hydrotheca tubular, free part roughly cylindrical; diameter distinctly decreasing basally at adnate part. Hydrotheca smoothly curved outwards, sometimes with marked inflection point where it becomes free. Hydrotheca adnate to internode for half or less of its adcauline length. Adcauline wall faintly convex at free part, a little more at adnate part. Abcauline wall concave by the middle, practically straight at basal and distal thirds. A ring of desmocytes present at base of hydrotheca. Hydrothecal aperture circular, directed up- and outwards. Rim even, with up to four renovations. Measurements (in µm). Hydrothecae: abcauline wall 1300–1350, free part of adcauline wall 600–750, adnate part of adcauline wall 810–900, adcauline wall 1500–1630, diameter at aperture 240–310, diameter at base 120. Cnidome: larger microbasic mastigophores, range 20–22 x 7.5–9, mean 21.3±0.7 x 8.1±0.4 (n=10); ratio, range 2.4–2.8, mean 2.6±0.1 (n=10); smaller microbasic mastigophores 8 x 3.5 Remarks. Acryptolaria longitheca resembles A. corniformis in the shape of the hydrothecae, although they are distinctly smaller in the former. Conversely, the nematocysts are larger in A. longitheca. Acryptolaria longitheca is close to A. frigida in the size of hydrothecae and nematocysts and some hydrothecae can be similar in their shape. Nevertheless, they are easily recognisable, because in the latter the hydrothecae are strongly curved outwards and adnate in more than half of its adcauline length (one-quarter to one-half free). In addition, the hydrotheca is almost completely cylindrical in A. frigida, its diameter smoothly decreasing at adnate part; the diameter reduction is much stronger in A. longitheca. Recently, Calder (2019) reported the species off Florida. His material agrees with the concept of A. longitheca, except for the more slender large nematocysts. Ecology and distribution. Species known from depths between 80.5 (Calder 2019) and 567 m (Allman 1877); present material at 112– 124 m. Peña Cantero & Vervoort (2010) reported it growing on corals and tubes of benthic organisms and with coppinia in February, and Calder (2019) found coppiniae in July. Acryptolaria longitheca has an uncertain distribution because only three previous records are considered valid: the original description by Allman (1877), off Double-Headed Shot Key, Western Atlantic, and those by Peña Cantero & Vervoort (2010), from the Loyalty Islands and Norfolk Ridge areas, and by Calder (2019), from the southwest coast of Florida. Present material comes from off Macquarie Island, in the South Pacific.

Acryptolaria crassicaulis (Allman, 1888) (Figs 1B, 5C) Cryptolaria crassicaulis Allman, 1888, lvii, lxvii, lxviii, 41, pl. 19, figs 3, 3a. Acryptolaria crassicaulis— Peña Cantero et al., 2007: 245–247, figs 6, 15D, 17E; Peña Cantero & Vervoort, 2010: 282–283, figs 6, 30; Peña Cantero & Horton, 2017: 7–8, fig. 3A–B. Material examined. Eltanin: 2/11 , four fragments up to 7 mm long (mounted on a microslide). Description. Hydrothecae alternate in two planes, making an obtuse angle. Internodes in a distinct zigzag pattern. Hydrotheca tubular, free part roughly cylindrical; diameter smoothly decreasing basally at adnate part. Hydrotheca curved outwards. Hydrotheca adnate to internode for about two thirds of its adcauline length. Adcauline wall convex. Abcauline wall concave at distal half, practically straight at basal half. Hydrothecal aperture circular, directed upwards and outwards. Rim even, with none or a few, quite long, renovations. Measurements (in µm). Hydrothecae: abcauline wall 1200–1300, free part of adcauline wall 520–640, adnate part of adcauline wall 900–1000, adcauline wall 1420–1600, diameter at aperture 220–250, diameter at base 100. Cnidome: larger microbasic mastigophores, range 14–15 x 4.5–5, mean 14.7±0.4 x 4.8±0.2 (n=5); ratio, range 2.9–3.3, mean 3.1±0.1 (n=5); smaller microbasic mastigophores 7 x 3. Remarks. Despite of the scarcity of material, it clearly belongs to this species, agreeing in the marked zigzag arrangement of internodes, the shape and size of hydrotheca, and the size of nematocysts (larger group 14–16.5 x 4.5–5.5 µm in the holotype). Acryptolaria conferta, whose hydrotheca is similar, and whose internodes are also arranged in a marked zigzag, has smaller hydrothecae and distinctly larger nematocysts. Ecology and distribution. Acryptolaria crassicaulis had been reported at depths between 236 (Peña Cantero & Vervoort 2010) and 2754 m (Peña Cantero & Horton 2017); present material at 2357 m. The species has been recorded with certainty off Ascension Island (07°54’20’’N, 14°28’20’’W) (Allman 1888) and from Rockall Trough and the Mid-Atlantic Ridge (Peña Cantero & Horton 2017), in the Atlantic Ocean, and from waters of the Loyalty Islands and New Caledonia (Peña Cantero & Vervoort 2010), in the Pacific Ocean. The present material, which constitutes the fourth confirmed record for the species, was collected at 49°33’S, 48°19’W, between the Falklands Islands and South Georgia, in the south-west Atlantic Ocean.