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Amphicocconeis ruatara Riaux-Gobin sp. nov. SEM Figs 49–61. Table 1 Description:— SEM. Valves oblong-elliptic to elongate, with slightly rostrate apices (Fig. 51). Axially bent in cingular view. Valve length 15 ± 2 µm, 14–17 µm. Valve width 6 ± 2 µm, 6–8 µm; L/ W 6.2 ± 0.8; n = 54 (SEM) (Table 1). SV convex with a concave narrow sternum (Figs 49–50). One row of large and transapically elongated areolae on each part of the sternum, one marginal row of dense and short areolae and, in between these two sectors, short areolae arranged more or less in quincunx. Often a low crest (or crista marginalis) delineating the marginal row of dense and short areolae, as a sort of short mantle (Figs 49–50, arrow). SV striae parallel in mid-valve, slightly radiate and denser on apices, uniseriate. SV striae 22 ± 3 in 10 µm. SVVC open, narrow (or sometimes larger), composed of short fused fimbriae (27 in 10 µm), separated from each other by an irregularly biseriate row of pores (Figs 52–54), festooned edge. Head pole of the SVVC with very short fimbriae. RV flat, dense striae composed of one narrow macro-areola, short supplementary marginal striae on mid-valve (Fig. 55). Raphe filiform. Proximal raphe endings externally simple and relatively close to each other, central nodule slightly elevated externally and unique for the genus (Figs 55–56, 59). Terminal raphe endings largely hooked on the mantle (Fig. 58). Raphe sternum somewhat elevated internally, with raphe slit slightly undulating. Proximal raphe endings simple and coaxial internally (Fig. 57). Central area small. RV striae 51 ± 6.5 in 10 µm; 42–60 in 10 µm. RVVC open, 30–50% valve width, 51 rows of uniseriate pores in 10 µm (Figs 60–61). Holotype:—Stub12 12/02/2020, BM001222887. Holotype specimen illustrated in Fig. 49. Syntypes:—Whole slide from the sample RAI 20, deposited at NHM (BM 81917 material). Etymology:—The specific epithet ruatara refers to the Ruatara rock (Raivavae Isl.) on the intertidal coastal environment where was first found the new taxon. Locality:—Ruatara rock (‘Rocher de l’Homme’), Raivavae (Austral Islands, South Pacific), RAI 20 and RAI 18 (intertidal red macroalgal turfs on fissures of the rock). Geo localization: S 23° 51.274’; W 147° 39.595’; T°C 23°.7, salinity Remarks:—Some similarities of A. ruatara sp. nov. with A.discrepans (A.W.F.Schmidt) Riaux-Gobin, Witkowski, Ector & Igersheim (Riaux-Gobin et al. 2018: figs 15–16), but with some differences: The axial rows of SV areolae on each part of the sternum are larger on A. ruatara than on A. discrepans, along with (in most cases) the presence of a crista marginalis delineating a narrow mantle on the new taxon. The SVVC in A. ruatara has short fused fimbriae with irregularly uni- to biseriate rows of pores, in contrast with a marginal row of one small pore in A. discrepans. The RVVC of A. ruatara shows dense uniseriate rows of pores (51 in 10 µm), while showing one marginal and elongate pore in A. discrepans (30–31 in 10 µm; Riaux-Gobin et al. 2018: figs 17–20)., Published as part of Riaux-Gobin, Catherine, Garcia, Marinês, Witkowski, Andrzej, Saenz-Agudelo, Pablo, Coste, Michel & Daniszewska-Kowalczyk, Genowefa, 2021, New Amphicocconeis (Bacillariophyta) from Raivavae and Tahiti Islands (South Pacific) and Porto Belo (Brazil), with re-examination of Psammococconeis, pp. 30-54 in Phytotaxa 513 (1) on pages 49-52, DOI: 10.11646/phytotaxa.513.1.2, http://zenodo.org/record/5306935, {"references":["De Stefano, M., Sacchi, U., Totti, C. & Romero, O. E. (2006) Cocconeis distans Gregory and Amphicocconeis debesi (Hustedt) De Stefano comb. nov. (Bacillariophyta), an intricate taxonomical history. Botanica Marina 49: 438 - 449. https: // doi. org / 10.1515 / BOT. 2006.055","Riaux-Gobin, C., Ector, L., Witkowski, A. & Igersheim, A. (2018) Achnanthales from historical Grunow collection in Porto Subzanski, Croatia. Botanica Marina 61 (6): 573 - 593. https: // doi. org / 10.1515 / bot- 2018 - 0045","De Stefano, M. & Marino, D. (2003) Morphology and taxonomy of Amphicocconeis gen. nov. (Achnanthales, Bacillariophyceae, Bacillariophyta) with considerations on its relationship to other monoraphid diatom genera. European Journal of Phycology 38: 361 - 370. https: // doi. org / 10.1080 / 09670260310001612646","Ehrenberg, C. G. (1838) Atlas von Vier und Sechzig Kupfertafeln ze Christian Gottfried Ehrenberg uber Infusionsthierchen. pp. pls I- LXIV. Leipzig: Verlag von Leopold Voss."]}

Amphicocconeis catharinensis Riaux-Gobin & Garcia. SEM, Figs 7–17. Table 1 Description:— SEM.Valves robust, oval-elliptic, with round apices. Valve length 18 ± 3 µm, 14–22 µm. Valve width 11 ± 2 µm, 9–13 µm; n = 10 (SEM) (Table 1). SV: surface convex, striae radiate and regularly spaced, uniseriate, composed of large rectangular areolae. On the valve face, each areola is positioned on the bottom of a depression with opening bordered by digit flaps (Figs 8–9). Areolae are internally closed by hymenes (Figs 10–12). On the mantle, each oblong areola is separated from the next by a granular and concave plain structure of triangular to rectangular shape (Figs 8–9, arrows). Short marginal striae not observed. 11 ± 1 SV stria in 10 µm. SVVC relatively narrow with big pores corresponding to each areola. RV: surface flat, striae radiate, composed of macro-areolae (large along the margin, short along the raphe, with short areolae dispersed in between, Fig. 13). Terminal-distal raphe endings strongly curved on same side (Figs 13, 15). Proximal raphe endings slightly enlarged and curved on same side (opposite to the terminal raphe endings, Fig. 16). 26 ± 2.5 RV stria in 10 µm. RVVC 1/4 of the valve width, with marginal transapical oblong pores corresponding to each macro-alreola (Fig. 17, twin arrowheads). Remarks:—The SV of Amphicocconeis catharinensis was illustrated as being the SV of Psammococconeis disculoides in Garcia (2001: figs 21, 23). The specific ornamentation of the SV mantle, with a concave structure in between each oblong areola (Figs 8–9) seems unique. The RV of A. catharinensis has some similarities with that of A. disculoides and A. debesi (large area with short radiate macro-areolae), but these short areolae in median-area are in very low density in A. catharinensis (Fig. 13), furthermore the SV of A. catharinensis is highly dissimilar to that of Amphicocconeis disculoides (Hustedt) De Stefano & Marino (figs 2–3, 6– 7 in De Stefano & Marino 2003; Figs 1). Type locality:—Zimbros, Peninsula do Porto Belo, Santa Catarina State, Brazil. Holotype:—Stub 4 19/06/2020, BM001222889. Holotype specimen illustrated in Fig. 7. Etymology:—The epithet refers to the location of the type habitat of this taxon in Brazil (locality Santa Catarina State).

Amphicocconeis cf. mascarenica Riaux-Gobin & Compère, 2011 (Figs 62–67). Table 1 Remarks:—The measurements and features of the specimens from the Pacific islands (Raivavae, Tahiti and Moorea Isls, Table 1) are close to those from the Mascarenes (Riaux-Gobin et al. 2011: tabl. 2), i.e., with valvocopulae with regularly biseriate rows of simple pores. This taxon is dominant on the Society Archipelago (Tahiti and Moorea Isls) as well as in the Austral Archipelago (Raivavae Isl.). In Tuamotu and Marquesas Archipelagos, Amphicocconeis are less abundant, but with, here again, A. cf. mascarenica as dominant taxon (pers. obs.)., Published as part of Riaux-Gobin, Catherine, Garcia, Marinês, Witkowski, Andrzej, Saenz-Agudelo, Pablo, Coste, Michel & Daniszewska-Kowalczyk, Genowefa, 2021, New Amphicocconeis (Bacillariophyta) from Raivavae and Tahiti Islands (South Pacific) and Porto Belo (Brazil), with re-examination of Psammococconeis, pp. 30-54 in Phytotaxa 513 (1) on page 52, DOI: 10.11646/phytotaxa.513.1.2, http://zenodo.org/record/5306935, {"references":["Riaux-Gobin, C., Compere, P. & Al-Handal, A. Y. (2011) New Amphicocconeis species off Mascarenes (Western Indian Ocean) and related taxa. Diatom Research 26 (2): 175 - 188. https: // doi. org / 10.1080 / 0269249 X. 2011.597958"]}

International audience; First described from the Mascarenes (Rodrigues Island, Indian Ocean), Olifantiella gorandiana Riaux-Gobin was later observed from several other oceanic basins. We here examine the morphology of this taxon from a scraping of a juvenile green turtle Chelonia mydas Linnaeus, named ‘G5-Manahere’, from Moorea Island (Society Archipelago, South Pacific). In this sample, a great range of morphologies, not previously described for the species, were encountered, demonstrating a high degree of polymorphism with regard to valve shape and also stria pattern. These morphological differences appear to be associated with size, as smaller cells become more rounded. The fine structure (e.g., stria density and pattern) may also be associated with changes in shape. These specimens may all belong to the same and unique taxon: Olifantiella gorandiana. This high degree of polymorphism is described, and put into the context of the constraining epizoic conditions. This study permits furthers the description of the fine structure of O. gorandiana, using focused ion beam (FIB) and scanning electron microscopy (SEM) techniques.

The Neretva River delta (surface area 170 km2) is situated on the eastern coast of the Middle Adriatic Sea. There are three lakes along the delta edges: Modro Oko, Desne and Kuti. These lakes are karstic cryptodepressions. The water masses of the lakes originate mostly from numerous subterranean karstic springs, which are situated along the perimeter edges. Lakes Modro Oko and Desne are influenced slightly by seawater (≤ 3 psu) from the Adriatic Sea. Seawater has no influence on Lake Kuti. Among all physical-chemical parameters, the studied lakes differed in temperature and NO3 concentrations. The aim of the present study is to determine the planktonic diatoms of the lakes and to examine its temporal distribution in relation to key environmental factors. In the period from 1994-1998, samplings were gathered throughout the seasons. Diatoms appeared to be the most important algal group in all three lakes. A total of 143 diatom taxa of were recorded in lakes over an approximate four-year period. The highest taxa were recorded in Lake Desne (96), and the lowest in Lake Kuti (50). The highest diatom cell numbers were noted in spring and the lowest in summer. In total, 45 taxa were registered for the first time in Croatian diatom flora.

The objectives of this research were to investigate the physical-chemical conditions in the water column and to describe the plankton diatom communities in these estuaries. The whole water column was well aerated in the ORE, since hypoxia or anoxia was noted below eight meters in the NRE. The euphotic layer in both estuaries decreased in the summer-autumn period. The concentration of all measured nutrients in the NRE was from 1.9 (for NO3) to 10.1 (for PO4) times higher than in the ORE. A total of 74 and 20 diatom taxa were recorded in NRE and ORE, respectively. Diatom abundance oscillated from 30 - 7.9 x 106 cells L-1 in the NRE, and from 20 - 8.7 x 103 cells L-1 in the ORE. Diatoms were the most important algal group throughout the year in the NRE, which contributed by 49-99% to microphytoplankton cell numbers. On the other hand, diatoms prevailed in the ORE only in November 1999, and in March and November 2000. The diatom communities in estuaries are of marine origin. The surface layer (0-2(-4) m) showed some fresh and brackish water taxa (Asterionella formosa, Fragilaria crotonensis and others), but they were present at background levels. In the NRE, the most important taxa in terms of cell numbers were Thalassiosira sp., Cerataulina pelagica, Chaetoceros compressus, Ch. curvisetus, Hemiaulus hauckii, Leptocylindrus danicus, Nitzschia longissima and Cyclotella sp. In the ORE, they were Nitzschia longissima and Chaetoceros spp. Nitzschia longissima was the most abundant (103-106 cells L-1) diatom taxa in both estuaries. These dynamic ecosystems are characterized by very frequent and rapid changes in environmental conditions. The main feature of diatom assemblages is the simultaneous dominance of more than one species. Our studies stress the important role of nutrients in the community structure.