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A striking abundance of cryptic and pseudocryptic species was highlighted in marine invertebrates by a number of studies, the majority of which focused however on cryptic diversity as such, without inferring on evolutionary drivers involved in organism diversification. The widespread polychaete Syllis gracilis Grube, 1840 was identified as a possible species complex by MALTAGLIATI et al. (2000), who identified Mediterranean marine and brackish populations as putative cryptic species on the basis of allozyme data. More recently, sequence data allowed to consider the allegedly cosmopolitan S. gracilis as a paraphyletic species complex, including at least three distinct Mediterranean lineages. To understand the role of biogeographical and ecological factors in the differentiation of the complex, populations of S. gracilis were sampled from eleven Mediterranean localities, and a combined morphological and molecular characterisation was carried out. Multivariate and univariate analyses on the morphological dataset highlighted that the majority of traits are fixed at population level, but it is possible to distinguish two morphotypes, one with short cirri, associated with intertidal coralline algae, and one with long cirri occurring on Sabellaria reefs and in brackish environments. On the other hand, 16S rDNA sequences highlighted the occurrence of three separated lineages, of which only two correspond to those identified by Álvarez-Campos et al. (2017). Therefore, S. gracilis includes at least four cryptic lineages. Molecular lineages did not show any correspondence with morphological diversity, and natural populations of S. gracilis usually included at least two cryptic lineages, without a clear distinction between marine and brackish-water populations. This outcome suggests that the relationship between the molecular pattern detected and ecological and biogeographical features is not straightforward. The observed morphological pattern is most likely due to local adaptations and phenotypic plasticity, while the separation between molecular lineages is possibly due to ancient geological events. The diversity and evolution of marine invertebrates is shaped by a number of different processes working and interacting at different spatial and temporal scales. The reconstruction of evolutionary processes should therefore take into consideration as many different evidence lines as possible. Although the inconsistent pattern detected make the integration of morphological and molecular patterns difficult, these patterns are the consequence of unpredictable interactions between different evolutionary drivers, thus representing an interesting case of irreducible evolutionary complexity in marine systems.

Accurate assessments of biodiversity are crucial to advising ecosystem-monitoring programs and understanding ecosystem function. Nevertheless, a standard operating procedure to assess biodiversity accurately and consistently has not been established. This is especially true for meiofauna, a diverse community (>20 phyla) of small benthic invertebrates that have fundamental ecological roles. Recent studies show that metabarcoding is a cost-effective and time-effective method to estimate meiofauna biodiversity, in contrast to morphological-based taxonomy. Here, we compare biodiversity assessments of a diverse meiofaunal community derived by applying multiple taxonomic methods based on comparative morphology, molecular phylogenetic analysis, DNA barcoding of individual specimens, and metabarcoding of environmental DNA. We show that biodiversity estimates are strongly biased across taxonomic methods and phyla. Such biases affect understanding of community structures and ecological interpretations. This study supports the urgency of improving aspects of environmental high-throughput sequencing and the value of taxonomists in correctly understanding biodiversity estimates.

Nematoplana cannoni sp. nov. (Žgures 2, 8D) Material examined HOLOTYPE: Australia, Queensland, Coolangatta, Rainbow Beach, lower intertidal in Žne sand (July 1993), whole mount (lactophenol) (G21182 2). Etymology The species is dedicated to Lester R. G. Cannon (Brisbane Museum), in recognition of his eOEorts to promote knowledge of Australian Platyhelminthes. Description The holotype is an adult worm, colourless, about 2 mm long in Žxed condition. With two pigmented eye-spots, enclosed within the brain capsule. The pharynx, short and collar-shaped, is located in the posterior Žfth of the body. Male genital organs. About 60 testes arranged in two irregular rows between vitellaria in front of the pharynx. The copulatory organ consists of two partly fused seminal vesicles, and an elongate muscular bulb (about 90 Mm long), provided with a copulatory stylet. The long seminal vesicles enter the bulb proximally. They are fused caudally for about one-third of their length. The spermiducts enter the seminal vesicles anteriorly. The stylet is a funnel-shaped structure, with a broad, oblique proximal opening and a narrow distal opening. The stylet is 38 Mm long. Its elongate base is about 25 Mm long, with a maximum width of 11 Mm. Ventrally, the stylet is provided with a narrow apophysis (about 15 Mm long). The apophysis is inserted at an angle of about 45ss with the main axis of the stylet. Both in living and Žxed conditions, it appeared angled in its distalmost part (Žgure 8D). Numerous, thick longitudinal muscles, most of which are connected basally with the musculature surrounding the bulb, are attached to the apophysis. The distal end of the stylet narrows above the apophysis into a slightly recurved tube, about one-third of the total length of the stylet. It is provided with a short tip (about 12 Mm long), where the narrow distal opening is located. The distal tip is perpendicular to the main axis of the stylet, and ends in a short, slightly curved terminal spike. Female genital organs. With two oocytes, arranged in a median row in front of the pharynx. Vitellaria stretch from behind the brain to in front of the ovaries; and from behind the pharynx to the level of the copulatory bulb. The oviducts fuse behind the bulb into a short common female duct, which opens to the outside through a female pore, medially between the seminal vesicles. Discussion The stylet of the new species, distinctly claw-shaped, with a short distal tip, and a comparatively long, oblique apophysis, is similar to that of the N. coelogynoporoide s species group (which includes N. coelogynoporoide s Meixner, 1938, N. ciliovesiculae Tajika, 1979 and N. riegeri Curini-Galletti and Martens, 1992) (cf. Curini-Galletti and Martens, 1992). However, no other Nematoplana has an apophysis which is angled distally. Furthermore, among the N. coelogynoporoide s group, the smallest stylet (that of the Mediterranean N. riegeri, which is about 60 Mm long) is still distinctly larger, with a slender base, and a proportionally longer portion of the stylet above the apophysis than that of N. cannoni. The Indo-PaciŽc member of the group (the Japanese N. ciliovesiculae) has a stylet somewhat similar in general shape to that of the new species, but markedly larger (about 130 Mm long), and with a relatively short, obtuse, straight apophysis. Members of the species group are furthermore much larger at maturity (> 10 mm), and have two rows of two to four isolated oocytes in front of the pharynx. The stylet of N. cannoni is somewhat similar in size and overall shape to that of N. nigrocapitula Ax and Ax, 1974, from Galapagos Is., which, however, has a shorter apophysis, not angled, a broader and straighter distal part, and a longer, straight terminal spike. Nematoplana nigrocapitula is furthermore distinct for its cephalic pigmentation, and for the presence of cnidosacs, cephalic gut and chorda intestinalis (Ax and Ax, 1974).

Nematoplana martensi sp. nov. (Žgures 3, 4A, 8F) Material examined HOLOTYPE: Australia, Queensland, Green Island, intertidal in medium to coarse coralline sand (September 1993), whole mount (lactophenol): G211823. PARATYPES: same data as holotype, one whole mount (lactophenol) (G211824); one specimen sagittally sectioned (G211825). Etymology The species is dedicated to Paul M. Martens (Hasselt, Belgium), in recognition of his contribution to the knowledge of the Proseriata. Description Animals colourless, comparatively rather large: the holotype is about 5 mm long; paratype G211824 is over 7 mm long. Anterior end elongate, provided laterally and terminally with sensory bristles. Posterior end with few adhesive glands. With two pigmented eye-spots, enclosed within the brain capsule. Epithelium entirely ciliated (cilia ranging from 2 to 3 Mm), with non-depressed nuclei. The distal edge of the epithelial cells appears strongly eosinophilous. Subepidermal longitudinal musculature well developed on the ventral side. The gut extends posteriorly nearly to the caudal tip of the body, and, anteriorly, to just behind the brain. The pharynx (Žgure 4A) is located in the posterior Žfth of the body. It is very short and collar-shaped. Its epithelium has depressed nuclei, and is ciliated except for a small area at the distal tip, where few pharyngeal glands discharge. The nuclei of these pharyngeal glands are located well outside the pharynx itself. Pharyngeal cilia are about 1.5 Mm long. No oesophageal area could be seen. With subepidermal, longitudinal external and much weaker, inner circular musculature. The pharyngeal cavity is narrow, and opens to the outside through the mouth. The epithelium of the pharyngeal cavity is unciliated, with non-depressed nuclei. Male genital organs. Numerous testes irregularly arranged laterally among vitellaria, in front of the pharynx. The copulatory organ consists of a single seminal vesicle, and a bulb provided distally with a stylet. The seminal vesicle is narrowly elongate, and provided with a thick coating of circular musculature. The spermiducts enter the vesicle anteriorly. In one of the specimens (G21182 4) sperm was not visible in the seminal vesicle, which was apparently degenerating. The seminal vesicle enters the bulb at its proximal base. The bulb is ovoid in shape (about 70 Mm high and 34 Mm wide in the holotype). It is lined with a thick coating of circular musculature, and provided with numerous prostatic glands, some of which have their nuclei outside the bulb itself. The stylet is thin and diaphanous, shaped as an elongate truncated cone, slightly in ated proximally. It is about 40 Mm high in the holotype, with a proximal opening 17 Mm wide, and a distal opening 9 Mm wide. Stylet of paratypes G211824 and G211825 are larger (respectively 60 Mm and about 55 Mm in length). The distal opening is minutely denticulate, and provided with a spike, about 6 Mm long in the holotype, and about 9 Mm in G211824. Due to the diaphanous condition of the stylet, this spike is di cult to see in Žxed mounts. In living animals, it is apparently held in the sagittal plane, since it could only be seen during torsions of the caudal part of the body. The male antrum opens to the outside through a narrow male pore, which is located close to the mouth. Female genital organs. With two ovaries, consisting of one mature oocyte each, laterally in front of the pharynx. Vitellaria stretch from behind the brain to in front of the ovaries. The oviducts fuse at the level of the copulatory bulb into a common female duct, which is lined by an unciliated epithelium with non-depressed nuclei, and opens to the outside through a female pore, surrounded by numerous, long female glands, posterior to the male pore. Discussion The species is characterized by its stylet, shaped as an elongate, truncated cone, provided distally with a spike, and lacking an apophysis. Such morphology is unique in the genus, and allows immediate discrimination. Nematoplana pullolineata Tajika, 1979 has a tubular stylet without apophysis; the tube is however slightly recurved, with both openings markedly oblique, without a distal spike, and its distal opening is not denticulate. Furthermore, the species is provided with a cephalic gut and chorda intestinalis (Tajika, 1979). The stylet of N. martensi is unusual in being very thin and diaphanous, and easily deformable. This, together with its diOEerential degree of maturity, may account for the remarkable diOEerence in size among holotype and paratypes.

Nematoplana ezoplanoides sp. nov. (Žgures 7, 8E, L; table 2) Material examined HOLOTYPE: Australia, Queensland, Mackay, Shoal Point, lower intertidal in coarse sand (July 1996), whole mount: (lactophenol): G211829. PARATYPES: same data as holotype, three specimens sagittally sectioned (G211830 –2). Other material. Four specimens from the type locality studied karyologically (July 1996). Etymology The species is named after the superŽcially similar genus Ezoplana Tajika, 1982. Description A medium-sized Nematoplana: the holotype is an adult worm, about 4.3 mm long in Žxed condition, without pigment or pigmented eye-spots. Anterior end elongate, provided laterally and terminally with sensory bristles. Epithelium with non-depressed (intra-epithelial) nuclei, and entirely ciliated. Cilia about 4 Mm long. Brain ovoidal, surrounded by a thin membrane. Mature specimens had two collar-shaped pharynges, lying close together. The posterior pharynx was larger, weaker and degenerating in most specimens. The anterior pharynx was smaller, and in most specimens clearly still in stages of formation. Juveniles had only one pharynx. Pharynges are located in the posterior seventh of the body. Male genital organs. Few testes irregularly arranged among vitellaria in front of the pharynx. The copulatory organ consists of two partly fused seminal vesicles, and a bulb provided distally with a stylet. The two seminal vesicles enter the bulb at its proximal base. Anteriorly, they are lined with a thin epithelium, surrounded by a thick layer of circular muscles. The muscular coating ends abruptly after about 60 Mm in the holotype. Posteriorly, the vesicles become much narrower, and they fuse caudally into one common vesicle, lined with a thin epithelium. Spermiducts enter the seminal vesicles anteriorly. The nuclei of spermatozoa are elongate, and spirally coiled. The bulb is ovoid (about 45 Mm high in the holotype). It is lined with a thick coating of circular musculature, and provided with numerous prostatic glands. The stylet is a funnel-shaped, intracellular, sclerotized structure, with a broad, oblique, ventral proximal opening and a narrow distal opening. The stylet is 37 Mm high in the holotype (measuring 40 and 41 Mm in the two semi-squashed karyological mounts). The base is about 21 Mm high in the holotype, with a maximum width of about 11 Mm. A at apophysis (about 15 Mm long) is present. It is almost of constant width along all of its length. A thick bundle of longitudinal muscles is connected proximally to the circular muscle sheath surrounding the bulb, and distally to the apophysis. The distal part of the stylet above the apophysis narrows abruptly into a nearly straight tube, about 12 Mm long. It is provided distally with a straight distal tip, orthogonal to the main axis of the stylet, and ending in a spike about 8 Mm long. The dorsal side of the stylet is thickened, particularly above the apophysis. The distal part of the stylet protrudes into a narrow male antrum, apparently unciliated. The antrum opens to the outside through a male pore, which is located close to the mouth. Female genital organs. With two, large, isolated oocytes medially in front of the pharynx. Vitellaria stretch from behind the brain to in front of the ovaries. The oviducts fuse at the level of the copulatory bulb into a common female duct, which opens to the outside through a female pore, surrounded by female glands. Karyotype. With n 53. Chromosomes diOEer only slightly in size. Chroms 1 and 2 are metacentric; Chrom. 3 is submetacentric, at the lower border of the class (Žgures 7C, 8L, table 2). Discussion Among the Unguiphora, the presence of two pharynges over at least part of the life cycle is among the deŽning features of the genus Ezoplana (Tajika, 1982). However, the position of the new pharynx diOEers: in front of the ovaries and much more anterior than the old one in Ezoplana; posterior to the ovaries and close to the old one in N. ezoplanoides. Furthermore, the new species has none of the other diagnostic features of the genus Ezoplana (i.e. presence of one pair of seminal receptacles in front of the (posterior) pharynx; stylet characteristically base-less, consisting only of an apophysis and a tubular, elongate, angled distal part) (Tajika, 1982, 1988). On the contrary, it presents the diagnostic feature of the genus Nematoplana, i.e. the partial, posterior fusion of the seminal vesicles, and is hence considered as such. There are reports of pharynx degeneration during or after sexual maturity in other species of the genus Nematoplana and in Tabaota curiosa Marcus, 1950 (Marcus, 1950; Sopott, 1973; Ax and Ax, 1974; Ehlers and Ehlers, 1980; personal observation), but simultaneous formation of a new pharynx has never been observed. A life cycle which includes degeneration and reconstitution of the pharynx, may however be more widespread in the Unguiphora than hitherto hypothesized, and possibly linked to the long life span (in some cases partly biennial) of (at least some of) its representatives (Sopott, 1973; Ax, 1977). In any case, the presence of both pharynges (in various stages of development/degeneration) in adult stages of the new species, is unique in the genus, and allows immediate recognition. Furthermore, its chromosome number (n 53) is peculiar to the new species, and the lowest known among the Unguiphora. The stylets of N. ezoplanoides and N. cannoni are somewhat similar in size and general shape. However, in N. cannoni the base is slimmer, and the peculiarly angled apophysis is inserted at 45ss with the main axis, while it is ap-like, and orthogonal to the main axis in the new species. Furthermore, the two species are immediately recognizable by the lack of pigmented eye-spots in the new species. The stylet of N. ezoplanoides is similar in size and shape to that of N. nigrocapitula, which however is pigmented, and is provided with eye-spots, cnidosacs, cephalic gut and chorda intestinalis. Nematoplana ezoplanoides, N. cannoni and N. rubra share a unique feature for the genus Nematoplana, i.e. the presence of only two oocytes, arranged medially in a single row. However, at least in N. rubra, this seems to be a transitory stage, with the plesiomorphic condition occurring in part of the life cycle. The poor knowledge of life cycles of extra-boreal unguiphorids and the limitation of sampled specimens per species do not allow inferences on the signiŽcance of this feature. Therefore, on a cautionary basis, it has not been used for taxonomic purposes. It should also be mentioned that no obvious synapomorphy appears shared by any of the three species above., Published as part of Curini-Galletti, M., Oggiano, G. & Casu, M., 2002, The genus Nematoplana Meixner, 1938 (Platyhelminthes: Unguiphora) in eastern Australia, pp. 1023-1046 in Journal of Natural History 36 (9) on pages 1039-1041, DOI: 10.1080/00222930110039585, http://zenodo.org/record/5340820, {"references":["MARCUS, E., 1950, Turbellaria Brasileiros (8), Boletins da Faculdade de Filoso Ž a, Ciencias e Letras, Universidade de S. Paulo, Zoologia, 15, 5 - 192.","SOPOTT, B., 1973, Jahreszeitliche Verteilung und Lebenszyklen der Proseriata (Turbellaria) eines Sandstrandes der Nordseeinsel Sylt, Mikrofauna des Meeresbodens, 15, 1 - 106.","AX, P. and AX, R., 1974, Interstitielle Fauna von Galapagos VII. Nematoplanidae, Polystyliphoridae, Coelogynoporidae (Turbellaria Proseriata), Mikrofauna des Meeresbodens, 29, 1 - 28.","EHLERS, B. and EHLERS, U., 1980, Zur Systematik und geographischen Verbreitung interstitieller Turbellarien der Kanarischen Inseln, Mikrofauna des Meeresbodens, 80, 1 - 23.","AX, P., 1977, Life cycles of interstitial Turbellaria from the eulittoral of the North Sea, in T. G. Karling and M. Meinander (eds) The Alex. Luther Centennial Symposium on Turbellaria, Acta Zoologica Fennica, 154, 11 - 20."]}

Nematoplana hamata sp. nov. (Žgures 5, 8C) Material examined HOLOTYPE: Australia, New South Wales, Byron Bay, town beach, lower intertidal in medium sand (July 1993), whole mount (lactophenol): G21826. Other material. One immature from the type locality studied karyologically (July 1993). Etymology Named after the characteristically hooked shape (lat: hamatus) of the stylet. Description The holotype is about 5 mm long, colourless, entirely ciliated. With two pigmented eye-spots located within the brain capsule. The short, collar-shaped pharynx is located in the posterior Žfth of the body. Male genital organs. Numerous testes arranged in two irregular rows between vitellaria in front of the pharynx. The copulatory organ consists of an ovoid muscular bulb (about 85 Mm high and 40 Mm wide), provided with a thick outer coating of circular and inner longitudinal musculature, connected basally to a single seminal vesicle. No sperm were seen within the vesicle. Distally, the bulb is provided with a copulatory stylet. The stylet is tubular, and about 110 Mm long. The proximal end is slightly swollen, with a markedly oblique opening. The tube has a constant width (about 9– 10 Mm) for all of its length. The distal fourth of the stylet is bent at nearly 45ss. The distal opening is about 9 Mm in diameter, and is provided with a slit about 20 Mm long. Female genital organs. With two rows of three isolated oocytes each, laterally in front of the pharynx. Vitellaria stretch from behind the brain at the level of the seminal vesicle. Female pore behind the male pore. Karyotype. With n 58. Plates were unsuitable for a karyometrical analysis. Discussion The very long, narrowly cylindrical, distally angled stylet of the new species is unique in the genus. Nematoplan a hamata shares with N. martensi and N. pullolineata the absence of an apophysis. The stylet of N. martensi is, however, straight, distally denticulate, and with a distal spike (see above); that of N. pullolineata is smaller (about 30 Mm), and diOEerently shaped (with a proportionally much smaller distal angled part, and a nearly straight ventral side) (cf. Tajika, 1979)., Published as part of Curini-Galletti, M., Oggiano, G. & Casu, M., 2002, The genus Nematoplana Meixner, 1938 (Platyhelminthes: Unguiphora) in eastern Australia, pp. 1023-1046 in Journal of Natural History 36 (9) on pages 1036-1037, DOI: 10.1080/00222930110039585, http://zenodo.org/record/5340820, {"references":["TAJIKA, K. - I., 1979, Marine Turbellarien aus Hokkaido, Japan III. Nematoplana Meixner, 1938 (Proseriata, Nematoplanidae), Journal of the Faculty of Science of the Hokkaido University, Series VI, Zoology, 22, 69 - 87."]}

During a two-week workshop held at the Sven Lovén Centre for Marine Sciences on Tjärnö, an island on the Swedish west-coast, meiofauna was studied in a large variety of habitats using a wide range of sampling techniques. Almost 100 samples coming from littoral beaches, rock pools and different types of sublittoral sand- and mudflats yielded a total of 430 species, a conservative estimate. The main focus was on acoels, proseriate and rhabdocoel flatworms, rotifers, nematodes, gastrotrichs, copepods and some smaller taxa, like nemertodermatids, gnathostomulids, cycliophorans, dorvilleid polychaetes, priapulids, kinorhynchs, tardigrades and some other flatworms. As this is a preliminary report, some species still have to be positively identified and/or described, as 157 species were new for the Swedish fauna and 27 are possibly new to science. Each taxon is discussed separately and accompanied by a detailed species list.