Amphicocconeis, Riaux-Gobin, Catherine, Garcia, Marinês, Witkowski, Andrzej, Saenz-Agudelo, Pablo, Coste, Michel & Daniszewska-Kowalczyk, Genowefa, 2021

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 : 44-45

Amphicocconeis clypeus Riaux-Gobin & Witkowski sp. nov. SEM Figs 18–34 . Table 1

Description:— SEM.Valves robust, oval-elliptic, with round apices ( Figs 18–19 ). Valve length 19 ± 3 µm, 15–27 µm. Valve width 11 ± 2 µm, 9–14 µm; L/ W 1.71 ± 0.1; n = 29 (SEM) ( Table 1). SV: convex, striae radiate and regularly spaced, to very slightly denser on apices, uniseriate with marginal denser areolae (with short striae) ( Fig. 18 ). SV striae 11 ± 0.8 in 10 µm, 9–11 in 10 µm. SV: sternum narrow and straight, slightly convex. Areolae mostly round to oblong-elliptic, crater-like, with an irregular oblong-narrow and sinuous opening, similar to a sepia eye ( Fig. 20 ). Often (i.e., 25% of specimens) presence of small round warts around the ‘sepia-like’ openings. Areolae internally closed by a convex hymen ( Fig. 23 ), with no apparent slits. On both sides of the SV sternum, one straight row of quincunx and regular oblong areolae. Marginal areolae also arranged along a regular row, while in mid-half valve the areolae are of irregular length and position. The SVVC is open and extended (1/3 of the valve), composed of rows of large and round apertures ( Figs 18, 21–22 ). RV: robust and flat, striae radiate, regularly spaced. Each stria composed of two macroareolae: a short macroareola near the raphe and a longer marginal one. Externally and internally, a large lunarshape space devoid of ornamentation ( Figs 24–25, 27 ). RV striae: 27 ± 2 in 10 µm. Raphe filiform and straight. External proximal raphe endings relatively close to each other and slightly deflected in the same side ( Fig. 24 ), internally simple, slightly expanded, rather distant and coaxial ( Figs 26–27 ). Central area small and rhomboid ( Fig. 26 , internal view). Striae strongly radiate at mid-valve. Terminal raphe fissure largely hooked on the mantle ( Fig. 24 ). Helictoglossa small and unraised ( Fig. 28 ). RVVC extended, open, with marginal rows of more or less complex small pores (27 in 10 µm, Figs 31, 32, 34 ), each row of pores corresponding to a RV stria, large edge devoid of ornamentation ( Fig. 30 ). On the head pole of the RVVC, presence (in most specimens) of a ‘plow sock’-shaped structure ( Figs 30, 33 ).

Remarks:—15 SV were observed, with low morphological variability. Six RV were observed, among which one external view with eroded macro-areola hymenes showing the underlying advalvar side ornamentation of the RVVC ( Fig. 29 ), and one internal view with the RVVC still in place ( Fig. 25 ). The SV of A. clypeus sp. nov. shows some similarities with that of A. catharinensis sp. nov., but with some differences, such as the marginal short striae in A. clypeus, the mantle specific ornamentation in A. catharinensis , and the RVVC highly different within both taxa.

Type locality:—Sample ‘Papeete 4 Holothuria ’, Tahiti Nui West coast, Arué District, North of Tombeau du Roi (S 17° 31.405′, W 149° 31.106′), collected by scraping a large specimen of Holothuria atra , intertidal environment, by C. Riaux-Gobin, 24 October 2010.

Holotype:—Stub 1 27/04/2012, BM001222888. Holotype specimen illustrated in Fig. 18 .

Syntypes:—Slides BM101645, Natural History Museum, London, UK, ZU8/38, Hustedt collection, Bremerhaven. Type slide for Amphicocconeis clypeus from ‘Papeete 4 holoth’ yet sent to BM as the holotype of Astartiella societatis Riaux-Gobin, Witkowski & Romero (2013: 421 figs 2–6, 12–29).

Etymology:—The specific epithet clypeus refers to the SV shape resembling a robust shield.

Figures

FIGURES 18–23. Amphicocconeis clypeus sp. nov. SEM (material ‘Papeete 4 Holothuria’, from Tahiti, South Pacific). SV in external view with still partly connected SVVC in advalvar view (Fig. 18), note the marginal row of dense areolae. SV in oblique view, with a SV sternum slightly convex, with four copulae (Fig. 19), SVVC open, with large pores, abvalvar view (Figs 21–22), SV areolae in external view, with ‘sepia-like’ opening (Fig. 20), SV in internal view with areolae covered by convex hymenes (Fig. 23). Scale bars: 6 µm (Fig. 22), 5 µm (Fig. 18), 4 µm (Fig. 23), 3 µm (Fig. 19), 1 µm (Fig. 21), 600 nm (Fig. 20).

FIGURES 24–29. Amphicocconeis clypeus sp. nov. SEM (material ‘Papeete 4 Holothuria’, from Tahiti, South Pacific). RV in external view with interrupted macro-areolae delineating a large lunar-shaped area void of ornamentation (Fig. 24), note the eroded macro-areolae giving access to the abvalvar side of the RVVC with complex marginal pores (Fig. 29), RV in internal view with the RVVC still in place (Fig. 25), RV in internal view (Fig. 27), detail of the central area in internal view (Fig. 26), detail of the internal apex with unraised/low helictoglossa (Fig. 28). Scale bars: 5 µm (Figs 24, 27), 4 µm (Fig. 25), 2 µm (Figs 26, 28), 400 nm (Fig. 29).

FIGURES 30–34. Amphicocconeis clypeus sp. nov.SEM (material ‘Papeete 4 Holothuria’, from Tahiti, South Pacific).RVVC in abvalvar view, with rows or irregular pores, with a large edge devoid of pores (Fig. 30, arrowhead), note the plow-sock (Figs 30, 33, arrows) at the head pole of the RVVC and marginal convex border (Figs 30–31), RVVC in advalvar view, with complex pores (Figs 32–33). Scale bars: 4 µm (Fig. 33), 3 µm (Fig. 30), 1 µm (Figs 31, 34), 600 nm (Fig. 32).