taxonID	type	description	language	source
03CA87E1EA45FF8DFE35BC09FE39500D.taxon	description	From a pearl oyster farm in Gatavake Bay (owner Michel Teakarotu), Cocconeis sp. (Table 3, Figs 13 – 15) was found as subtidal, epizoic on Pinctada margaritifera, also present on ropes lying at the same depth (i. e. 15 m, Rik 15). This taxon had small dimensions, an oblong-elliptic to linear valve shape (Figs 13 – 14), blunt apices, measurements close to that in the C. mascarenica type (Table 3). Cocconeis sp. had short and dense dash-like SV areolae (up to 6 per stria, with no axial alignment), SV hymenes with marginal short slits (Fig. 15), and elliptic SV sternum. Valves measured 8.0 – 9.4 µm in length and 3.5 – 4.3 µm in width, with 32 – 36 SV striae in 10 µm, regularly spaced (no areolae on SV apex), and 39 – 45 RV striae in 10 µm, regularly spaced, with a marginal hyaline area and low with presence-absence, biotopes and location, presented as ‘ supplementary material’. Taxon acronym Achnanthales Achnanthes cf. brevipes Agardh acbre Achnanthidium glyphos Riaux-Gobin, Compère & Witkowski acgly Achnanthidium glyphos morph acgly 2 Achnanthidium pseudodelicatissimum Riaux-Gobin, Witkowski & Compère acpse Achnanthidium sp. aff. Achnanthes fogedii Håkansson acfog Amphicocconeis clypeus Riaux-Gobin & Witkowski amcly Amphicocconeis cf. mascarenica Riaux-Gobin & Compère ammas Amphicocconeis rodriguensis Riaux-Gobin & Al-Handal amrod Amphicocconeis ruatara Riaux-Gobin amrua Amphicocconeis sp. amsp Astartiella sp. assp Cocconeis angularipunctata Riaux-Gobin, Romero, Compère & Al-Handal coang Cocconeis cf. borbonica Riaux-Gobin & Compère cobor Cocconeis carinata Riaux-Gobin, Ector & Witkowski cocar Cocconeis coralliensis Riaux-Gobin & Compère cocor Cocconeis coronatoides Riaux-Gobin & Romero ‘ type’ cocid Cocconeis coronatoides discoid morph cocid 2 Cocconeis cupulifera Riaux-Gobin, Romero & Al-Handal cocup Cocconeis cf. delapunctata Hohn codel Cocconeis cf. diaphana W. Smith codia Cocconeis distans Gregory codis Cocconeis guttata Hustedt & Aleem cogut Cocconeis cf. geometrica Riaux-Gobin, Romero, Compère & Al-Handal cogeo Cocconeis heteroidea Hantzsch cohet Cocconeis margaritata Riaux-Gobin & Al-Handal comar Taxon acronym Cocconeis mascarenica Riaux-Gobin & Compère comas Cocconeis mascarenica forma conew Cocconeis cf. molesta Kützing comol Cocconeis paucistriata Riaux-Gobin, Romero, Compère & Al-Handal copau Cocconeis peltoides Hustedt copel Cocconeis peltoides var. archaeana Riaux-Gobin & Compère coarc Cocconeis placentula Ehrenberg complex copla Cocconeis pseudodiruptoides Foged copsd Cocconeis pseudograta Hustedt copsg Cocconeis pseudomarginata Gregory copsm Cocconeis santandrea Riaux-Gobin, Witkowski & Bemiasa cosan Coccconeis scutellum Ehrenberg coscu Cocconeis sigillata Riaux-Gobin & Al-Handal cosig Cocconeis suzukii Riaux-Gobin, Compère, Coste, Straub & Taxböck cosuz Cocconeis sp. 5 (= sp. 4 in Riaux-Gobin et al. 2015 c) cosp 5 Madinithidium flexuistriatum (Riaux-Gobin, Compère & Witkowski) mafle Madinithidium scalariforme (Riaux-Gobin, Compère & Witkowski) masca? Majewskaea Van de Vijver, Robert, Witkowski & Bosak maj Planothidium cf. delicatulum (Kützing) Round & Bukhtiyarova pldel Planothidium mathurinense Riaux-Gobin & Al-Handal plmat Planothidium rodriguense Riaux-Gobin & Compère plrod Planothidium sp 1 oblong without fascia plsp 1 Planothidium sp 2 elliptic sternum pls 2 Schizostauron citronella (Mann) Górecka, Riaux-Gobin & Witkowski sccit Olifantiella Olifantiella cf. rodriguensis Riaux-Gobin olrod Olifantiella pilosella Riaux-Gobin olpil	en	Riaux-Gobin, Catherine, Saenz-Agudelo, Pablo, Coste, Michel, Jordan, Richard W., Criobe-Uar, René Galzin (2025): Marine Achnanthales and Olifantiella from the Gambier Archipelago (South Pacific). Micronesica 2025 (1): 1-33, DOI: 10.5281/zenodo.16968387
03CA87E1EA45FF8DFE35BC09FE39500D.taxon	discussion	Remarks: Cocconeis mascarenica (Riaux-Gobin & Compère 2008) was originally compared to C. neodiminuta Krammer & Lange-Bertalot 1991 and to C. neothumensis Krammer 1990, but the RV of C. neothumensis (Krammer 1990, fig. 34) was also attributed to C. neodiminuta (Krammer & Lange-Bertalot 1991, pl. 55, fig. 3). Furthermore, the shape of the SV areolae in C. mascarenica differs from that of C. neodiminuta (ref. cit., pl. 55, fig. 1) in being much shorter, and the SV sternum in C. mascarenica being narrow-straight in place of largely elliptical ones. Note that a picture illustrating C. neothumensis in Krammer (1990, fig. 39) was also used to illustrate C. neodiminuta by Krammer & Lange-Bertalot (1991, pl. 55, fig. 1), causing taxonomic confusion between C. mascarenica and the two latter taxa. Furthermore, the freshwater taxa C. neodiminut a and C. neothumensis have dissimilar RV and SV stria densities, while C. mascarenica has the same stria density on both valves (see discussion in Riaux-Gobin et al. 2018). Also, there are some similarities with the later described C. neothumensis var. marina (De Stefano et al. 2000, figs 53 – 65), but with differences (see above remarks). In the original description of C. mascarenica off Mascarenes, the taxon demonstrated an obvious phenotypic plasticity, with two morphs described from Rodrigues (morphs 1 and 2 in Riaux-Gobin et al. 2011 c). The Cocconeis mascarenica complex probably includes several species that can only be separated via genetics. In addition, Cocconeis mascarenica and C. cf. mascarenica and all the above-mentioned morphs present in Mangareva (Tables 2 – 3, Figs 7 – 18) have some similarities with C. placentula sensu lato (as referred to by Potapova & Spaulding 2013), but with overall smaller valve dimensions, higher stria densities on both valves, and valvocopulae without conspicuous fimbriae [C. placentula sensu lato (see ref. cit. above) has 20 – 24 striae in 10 µm on RV, and 15 – 25 on SV]. Note that the bibliography of the C. placentula sensu lato complex is complicated, with several new taxa that can only be distinguished through SEM, such as the recently described C. fetscheriana Stancheva (2022, 128). The morphological plasticity in such taxa can also be pro parte imputed to the reproductive stages of the taxon (see Jahn et al. 2020), rendering cultures and genetics essential in definitively splitting taxa.	en	Riaux-Gobin, Catherine, Saenz-Agudelo, Pablo, Coste, Michel, Jordan, Richard W., Criobe-Uar, René Galzin (2025): Marine Achnanthales and Olifantiella from the Gambier Archipelago (South Pacific). Micronesica 2025 (1): 1-33, DOI: 10.5281/zenodo.16968387
03CA87E1EA48FF8CFECBBF79FE855213.taxon	description	An oblong-elliptic and relatively large taxon (Figs 23 – 30, Table 3), was common in the subtidal samples Rik 13, Rik 15 and Rik 16, and characterized by its SV short areolae arranged in a regular decussate pattern, with apical rows arranged along a 135 ° grid-pattern (Fig. 27, white lines). The open SVVC (Fig. 29, ellipse) has a smooth edge (Fig. 30, arrowhead). The SV sternum is narrow, irregular, concave, with a reduced to absent central area (Fig. 27 arrowhead). SV striae are more or less parallel in median valve and abruptly radiate near the apices (Fig. 28 arrowhead). At the apices, a marginal row of SV areolae are perpendicular to the margin. The RVVC was not observed. The RV fascia is narrow and straight, reaching the margins, and central raphe endings are close to each other (Fig. 24). Helictoglossae slightly curved (Fig. 26). RV areolae present at the apices (Figs 23, 25 – 26). This taxon is provisionally assigned to C. cf. diaphana Smith 1853 (see Remarks). Remarks: The latter taxon (Figs 23 – 30) has affinities with Cocconeis diaphana Smith var. diaphana, except for a RV fascia reaching both margins, and striae on both valves much denser than in the C. diaphana var. diaphana type (BM 23161, in Riaux-Gobin et al. 2016). We can also compare our images with those illustrating the iso-lectotype of C. diaphana Smith var. diaphana (mica labelled as Cocconeis diaphana n. sp., Jersey, Aug. 14 1852, deposited in the Van Heurck collection in Meise, in Riaux-Gobin et al. 2016, figs 21 – 26). In the latter taxon, the RV and SV stria densities are also dissimilar, being less dense than in the Mangareva taxon (Table 3). Furthermore, the SV and RV striae (in the iso-lectotype) are often marginally dichotomous while uniseriate until the margin in the Mangareva taxon. The latter also has some affinities with Cocconeis molesta, except for its larger dimensions, oblong shape, and RV fascia expanding up to both margins. Also, there are some affinities with C. molesta var. crucifera Grunow in Van Heurck (1880, pl. 30), as illustrated by Kobayasi & Nagumo (1985, figs 1 – 12), and by De Stefano et al. (2000, figs 33 – 36), but in the latter taxon, the RV fascia is much shorter, and the valve shape is less oblong than in the Mangareva taxon. Note that C. molesta var. crucifera was proposed as a synonym of C. molesta (Riaux-Gobin et al. 2016).	en	Riaux-Gobin, Catherine, Saenz-Agudelo, Pablo, Coste, Michel, Jordan, Richard W., Criobe-Uar, René Galzin (2025): Marine Achnanthales and Olifantiella from the Gambier Archipelago (South Pacific). Micronesica 2025 (1): 1-33, DOI: 10.5281/zenodo.16968387
03CA87E1EA49FF8EFDC8BCB3FD11511E.taxon	description	Stria densities and axial rows in 10 µm, length & width in µm. Taxon Length Width L / l RV SV str. SV axial RV str. rows fascia * Cocconeis cf. mascarenica not (n = 27) 7.2 4.1 1.76 37.8 40.6 always no *** Cocconeis mascarenica not (n = 31) 6.7 3.8 ca. 1.7 38 25 - 35 always no * Cocconeis sp. (n = 8) 7.8 3.8 2.08 38.8 37.2 no no decussate up * Cocconeis cf. diaphana (n = 12) 14.4 6.6 2.20 39.8 52.8 pattern margins half * Cocconeis cf. molesta (n = 5) 9.1 6.6 1.38 46.9 52.8 no valve in zig- ** Cocconeis molesta Kütz. BM ca. 30 zag 22 - <half 18381 (n = 4) LM 16.4 9.7 1.96> 30 23 valve ** Cocconeis diaphana W. Sm. in zig- var. diaphana BM 23161 zag ca. short, (n = 11) LM 33 - 42 21 - 26 1.65 25 26 23 elliptic ** Cocconeis diaphana W. Sm. short, Isolectotype SEM ca. 38 ca. 23 1.65 22 35 unclear elliptic ** Cocconeis dirupta W. Greg. ca. zig- <half BM 1420 (n = 16) LM 18 - 37 17 - 31 1.12 18.9 16.6 zag valve EPIZOIC DIATOM ASSEMBLAGES Rik 5 and Rik 16 were both cumulative scrapings of several individuals pertaining to a well circumscribed population of Holothuria atra collected in small areas (ca 3 m 2), 1) from Gatavake Bay (west Mangareva, Rik 5), 2) from Rikitea nearshore (east Mangareva, Rik 16). The two epizoic assemblages were highly dissimilar (Table 2), with a higher number of taxa in Rik 16 (Table 2). Note that the assemblage in Rik 7 (sediments close to the location of the holothurian scraping Rik 5) and in Rik 10 (sediments close to the holothurian scraping Rik 16), are also highly different from what was found in each holothurian’s population. Some taxa present on the holothurians were absent from the nearby environment and vice versa, but the species richness is similar among epizoic and non-epizoic assemblages, being higher for Rik 16 – Rik 10 (Rikitea environment) than for Rik 5 – Rik 7 (Gatavake Bay). There were no diatom taxa unique to a particular epizoic population, or particularly dominant with regards to its abundance in the nearby substrates. From a shallow and well-oxygenated zone (exposed intertidal zone), Rik 9, a scraping of several living specimens of Rochia nilotica (Syn.: Trochus niloticus Linnaeus 1767), (ca. 5 cm in length, colonized by diminutive filamentous algae and encrusting red algae, probably pertaining to Corallinaceae, Maggy Nugges comm. pers.), was quantitatively diatom-poor, but with the presence of large diatoms such as Achnanthes cf. brevipes Agardh 1824 and Cocconeis pseudodiruptoides Foged (1975, 18). Note that the latter taxon was only observed in Rik 9 (see supplementary material), possibly linked to the ethology of this mollusk migrating from intertidal to subtidal substrates, whereas the other studied samples (except for the pearl oyster farm samples) were strictly intertidal (<50 cm deep). The scraping of empty green-colored tubes of Teredo sp. (probably colonized by unicellular chlorophytes) was almost void of benthic diatoms. This driftwood was subjected to drastic conditions such as high light exposure and intermittent desiccation. The scrapings of living two-year old Pinctada margaritifera (‘ Black-lipped Pearl Oyster’), before grafting (before nucleus transplant) (Rik 12 – 14, Table 2), as well as a one-year old individual (Rik 14 bis), were surprisingly diatom poor, quantitatively and qualitatively, whereas the macroalgae living on mooring ropes at the same depth (Rik 15) were colonized by a diverse array of diatoms, apparently absent from the oyster’s fouling. This low diatom colonization may be related to the fact that the oysters were cleaned every 3 months (via a passage to kärcher, followed by scraping with a knife), which drastically lowers the biofouling potentially detrimental to the oyster growth. This biofouling was composed of macroalgae and small fauna (i. e. bryozoans, ascidians, sponges, see also Lacoste et al. 2021) potentially colonized by diatoms. Note that the subtidal assemblages from the pearl oyster farm (epizoic as well as epiphytic, Table 2) seem to be characterized by the presence of taxa absent in intertidal samples from the same bay, such as Schizostauron citronella (Mann) Górecka, Riaux-Gobin & Witkowski (in Górecka et al. 2021, 1480), Cocconeis pseudomarginata Gregory (1857, 492) and Cocconeis peltoides var. archaeana Riaux-Gobin & Compère (in Riaux-Gobin et al. 2011 d, 330). NMDS ANALYSES In order to visualize the level of similarity among samples or groups of samples as a function of their diatom assemblages, an NMDS analysis was carried out. The full data are given as supplementary material. Note that the NMDS is testing the grouping of samples in relation to their assemblage compositions, and not whether a certain taxon is a reflection of a particular biotope or ethology. The analysis illustrated the relationships between samples (Fig. 41). The epizoic assemblages (blue points in Fig. 41, upper diagram) slightly group (but not significantly, see PERMANOVA results below), while the other assemblages (epiphytic and epipsammic taxa) have no particular grouping (Fig. 11, upper diagram). Concurrently, the different locations and bathymetries appear to have a significant influence on the assemblages (see PERMANOVA results below) (Fig. 41, bottom diagram), with Hao atoll and Togegegie motu grouping together negatively, possibly due to the low species richness and particular calcic environment. The subtidal samples group positively on the left of the analysis (violet points, Fig. 41 bottom diagram) with a particular colonization in terms of species, as noted above in, for example Schizostauron citronella (Mann) Górecka, Riaux-Gobin & Witkowski and also Cocconeis coronatoides Riaux-Gobin & Romero ‘ discoid morph’ (acronym cocid 2, see supplementary material). The subtidal epizoic assemblage was slightly different from that growing as non-epizoic at the same depth (see supplementary material and violet point), but still grouping with the other subtidal samples. The samples from Gatavake Bay (red points, bottom diagram) group slightly differently from the samples from the Rikitea shore line (blue points). The PERMANOVA results provide a statistical basis for the above remarks, and indicate that the biotope (upper diagram) did not have a significant effect on the community dissimilarity (Permanova R 2 = 0.10, F = 1.14, 2 df, p-value = 0.262). In contrast, the effect of the location (bottom diagram) was statistically significant (Permanova R 2 = 0.42, F = 3.083, 2 df, p-value = 0.001). Furthermore, results from an ad-hoc pairwise comparison among locations (excluding location H - Hao atoll- because of its small sample size), indicated that site S (subtidal samples, pearl oysters) was statistically significant from the rest (p-values <0.01), site R (Rikitea) was statistically different from sites G (Gatavake Bay) and M (Totegegie motu) (p-value <0.01), and sites G and R were also statistically different (p-value <0.01).	en	Riaux-Gobin, Catherine, Saenz-Agudelo, Pablo, Coste, Michel, Jordan, Richard W., Criobe-Uar, René Galzin (2025): Marine Achnanthales and Olifantiella from the Gambier Archipelago (South Pacific). Micronesica 2025 (1): 1-33, DOI: 10.5281/zenodo.16968387
