Amphicocconeis catharinensis Riaux-Gobin & Garcia. SEM

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, Phytotaxa 513 (1), pp. 30-54 : 44

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).

Figures

FIGURES 7–12. Amphicocconeis catharinensis sp. nov. SEM (Brazilian material ICN n° 91485, Zimbros, Porto Belo, Brazil). SV in external view with a narrow sternum (Fig. 7), crater-like areolae with opening bordered by digit expansions (Figs 8–9, arrowheads), mantle ornamentation with oblong areolae and granulate depressions (Figs 8–9, arrows), SV internal views (Figs 10–12), with areolae closed by convex hymenes, SVVC with large pores (Figs 11–12, arrowheads), a part of the RV still present (Fig. 11, framed arrow). Scale bars: 5 µm (Figs 10–11), 4 µm (Fig. 7), 1 µm (Figs 8–9, 12).

FIGURES 13–17. Amphicocconeis catharinensis sp. nov. SEM (Brazilian material ICN n° 91485, Zimbros, Porto Belo, Brazil). RV in external view with marginal macro-areolae, short macro-areolae on each side of the raphe, and spread shorter areolae in between (Fig. 13), curved distal raphe endings (Fig. 15, arrowhead), proximal raphe endings curved in same side (Fig. 16), entire frustule showing the RV in internal view (Fig. 14), RVVC with oblong marginal pores in same number as the RV striae (Fig. 17, twin arrowheads). Scale bars: 4 µm (Figs 13, 17), 3 µm (Fig. 14), 1 µm (Figs 15, 16).

FIGURES 1–6. Amphicocconeis disculoides. SEM (Brazilian material ICN n° 91485, Zimbros, Porto Belo, Brazil). SV in external view with short marginal striae (Fig. 1), SV areolae along the SV sternum (Fig. 2), SV oblong areolae with irregular aperture (Fig. 3), SV in internal view, with SVVC still in place with clusters of pores (Figs 5–6, twin arrowheads and arrow), RVVC (Fig. 4, arrow), and a part of the RV still attached (Fig. 4, arrowhead). Scale bars: 7 µm (Fig. 4), 6 µm (Fig. 1), 5 µm (Fig. 5), 1 µm (Figs 3, 6), 700 nm (Fig. 2).