Cocconeis kurakakea Riaux-Gob. & Witkowski, 2018

Riaux-Gobin, Catherine, Witkowski, Andrzej, Jordan, Richard W., Parravicini, Valeriano & Planes, Serge, 2018, Cocconeis kurakakea, a new diatom species from Nukutavake (Tuamotu Archipelago, South Pacific): description and comparison with C. diruptoides and C. pseudodiruptoides, Phytotaxa 349 (2), pp. 115-129 : 118-121

Cocconeis kurakakea Riaux-Gob. & Witkowski , sp. nov. Figs 2 – 39

LM: Small valves (7–16 μm long), narrow (3–6 μm wide), rod-like, linear-elliptic (length/width ca. 2.4), SV sternum and raphe sigmoid. SV ( Figs 2 , 9–13 ) and RV ( Figs 3 , 4–8 ) striation almost indiscernible with the LM, only a decussate pattern is observed on SV specimens at high magnification ( Figs 2 , 9–13 ).

SEM: Sternum valve: Striae regularly spaced, slightly radiate ( Figs 14–16 ). SV areolae small, slightly elongate and decussate (no axial rows of SV areolae). Hexagonal areola pattern (i.e., honeycomb-like) with a decussate regular arrangement, as observed in a corroded SV ( Fig. 15 ). One marginal row of elongate areolae present ( Fig. 15 ); hyaline marginal area absent ( Fig. 15 ). SV sternum narrow ( Figs 14, 16 ), very slightly enlarged on central area before last quarter of valve ( Fig. 15 arrows). SV corroded areola hymenes ( Fig. 20 arrowhead) with probable slits perpendicular to the areola walls. SV marginal supplementary short striae present ( Fig. 16 arrowheads); often one stria slightly shorter in center, on one side of valve (not shown). Internal side: presence of a round to oblong foramina ( Figs 25–26 ). Marginal SV areolae covered (funnel-like, Fig. 25 arrow) with lateral foramina ( Fig. 25 arrowhead). Sternum valve valvocopula (SVVC, Figs 23, 27 arrowheads) as an open and imperforated large band, without fimbriae ( Figs 22, 24 arrow). SV sternum thickened ( Fig. 24 ). Cingulum composed of 4 narrow open copulae ( Figs 18 , 34 ), up to 6 (not shown). Raphe valve: Valve weakly silicified, flat to slightly concave ( Figs 29, 34 ). Striae regularly spaced, parallel to radiate close to apices, composed of small round areolae. One row of marginal slightly elongate areolae ( Fig. 32 arrowheads). Raphe sigmoid, proximal raphe endings straight, simple and close together, terminal raphe endings close to margin ( Figs 33–34 ). Short hemi-fascia ( Fig. 30 arrow), sometimes almost lacking ( Fig. 32 ). Axial area narrow. RV areolae externally closed by hymenes with radiate slits ( Fig. 35 ). Internally, raphe located in an elevated axial area ( Figs 36–39 ). Raphe valve valvocopula (RVVC) open ( Fig. 34 ), without fimbriae ( Fig. 38 arrowhead). Terminal raphe endings bent in opposite directions ( Fig. 36 ). No areolae on apices ( Fig. 39 ).

Diagnostic features of Cocconeis kurakakea sp. nov.: The new species is characterized by its small size, linear-elliptic shape, and RV and SV striae that are almost undetectable with the LM. Using the LM we can only distinguish the asymmetrical small RV fascia (hemi-fascia), the decussate pattern on the SVs and the sigmoid structure of the SV sternum and raphe. With the SEM, the SV areola structure and pattern, the RV hemi-fascia and high cingulum make the species easily distinguishable.

Types:— BM-101912 (holotype: BM), illustrated in Figs 2–3 ; specimen on SEM stub 1–310217 (illustrated in Fig. 16 ) and slide ‘NTV A1’ in collection C. Riaux-Gobin (isotype: CRIOBE, Perpignan , France, here designated) ; slide SZCZ 24377 in collection A. Witkowski (isotype: The Faculty of Geosciences , Szczecin, Poland, here designated) .

Type locality:—Nukutavake reef (Tuamotu Archipelago, 19°16′50″S 138°47′07″W). Sample ‘NTV A1’. Oct. 2016. Collector: Valeriano Parravicini.

Etymology:The epithet kurakakea refers to the marae Kurakakea, located in the village of Tavananui (Nukutavake, Tuamotu Archipelago). This marae (ancient sacred site where religious and tribal ceremonies were celebrated), the most important marae of the atoll, was destroyed by a cyclone in 1983.

Habitat: Undetermined filamentous green macroalgae on the coral reef slope.

Distribution: Presently, the new taxon is only recorded from Nukutavake, and hence may be narrowly endemic.

Figures

FIGURES 2–3. Micrographs (LM) of Cocconeis kurakakea: type population on Nukutavake (sample NTV A1). Fig. 2. Represents the SV (sternum valve). Fig. 3. Shows the RV (raphe valve) on the same frustule. Designated as the illustration of the holotype. Scale bar = 10 μm.

FIGURES 4–13. LM micrographs of Cocconeis kurakakea: the type population on Nukutavake (sample NTV A1). Figs 4–8. RVs with the asymmetrical small fascia (arrowheads). Figs 9–13. SVs with a decussate pattern. Scale bar = 10 μm.

FIGURES 14–20. SEM micrographs of Cocconeis kurakakea: the type population on Nukutavake (sample NTV A1), SV external views. Fig. 14. Entire SV showing (arrowhead) the open SVVC (sternum valve valvocopula). Fig. 15. Corroded valve with the decussate pattern of areolae and a marginal row of longer areolae, also showing the SV sternum with thickenings (arrows). Fig. 16. Entire SV with short marginal striae (arrowheads). Fig. 17. Detail of the SV apex and open SVVC (arrowhead). Fig.18. Cingulum with 4 open bands (numbered bands). Fig. 19. SV apex and open SVVC (arrowheads).Fig. 20. Corroded SV areolae with remaining hymen edge (arrowhead).Scale bars = 3 μm (14–15), 2 μm (16), 1 μm (17), 400 nm (18–19), 200 nm (20).

FIGURES 21–27. SEM micrographs of Cocconeis kurakakea: the type population on Nukutavake (sample NTV A1), SV internal views. Fig. 21. Entire SV with SV sternum thickenings and decussate areola pattern with oblong foramina. Fig. 22. SV valvocopula (SVVC) partially detached (arrow). Fig. 23. Open SVVC without fimbriae (arrow). Fig. 24.Apex with the SVVC irregular edge lying on the virgae (arrow). Fig. 25. SV margin with sort of funnel (arrow) opening by pores (arrowhead). Fig. 26.Areolae, internal oblong foramina (arrow), and hymenes located on the valve face (arrowhead). Fig. 27. SVVC open (arrowheads). Scale bars = 3 μm (22–23) 2 μm (21), 700 nm (27), 600 nm (24), 400 nm (25), 300 nm (26).

FIGURES 28–35. SEM micrographs of Cocconeis kurakakea: the type population on Nukutavake (sample NTV A1), raphe valve (RV) external views. Figs 28–29. RVs (raphe valves) with sigmoid raphe and multiple cingular bands. Figs 30–32. Detail of the RV central area with an asymmetric short fascia (30 arrow), and a marginal row of longer areolae (32 arrowheads). Fig. 33. Apex with the terminal raphe ending. Fig. 34. Open RV valvocopula (RVVC) without fimbriae (arrowheads), and cingulum with 4 bands (numbered). Fig. 35. RV areola hymenes with radiate slits. Scale bars = 2 μm (28–29), 1 μm (30–33), 700 nm (34), 100 nm (35).

FIGURES 36–39. SEM micrographs of Cocconeis kurakakea: the type population on Nukutavake (sample NTV A1), SV internal views. Fig. 36. Entire valve with sigmoid raphe. Fig. 37. Detail of the central area with an asymmetric short fascia (arrowhead). Fig. 38. Details of an apex, with bent terminal raphe ending and smooth edge of the RVVC (arrowhead). Fig. 39. Round small RV areolae with short slits (arrowhead). Scale bars = 2 μm (36), 1 μm (37–38), 600 nm (39).