Amphicocconeis antiqua Riaux-Gobin & Coste, 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 : 45-49

Amphicocconeis antiqua Riaux-Gobin & Coste sp. nov. SEM Figs 35–48 ; Table 1

Description:— SEM. Valves robust, fusiform to slightly rhomboid, with ogival apices ( Figs 35, 36, 39 40 ). Valve length 18 ± 3 µm, 15–24 µm. Valve width 10 ± 2,8 µm, 8–17 µm; L/ W 1.8 ± 0.2; n = 16 (SEM) ( Table 1). SV: convex, striae radiate and regularly spaced, uniseriate ( Figs 35–36 ). SV striae 11.5 ± 2 in 10 µm, 9–14 in 10 µm. Areolae oblong-elliptic, crater-like, with an oblong-narrow and straight opening ( Fig. 37 ). Areolae internally closed by a convex narrow hymen. Externally, on both sides of the SV sternum, one row of cupules along an elliptic frame ( Fig. 35 , arrows). No marginal short-intercalary striae. SVVC open, simple with short fimbriae ( Fig. 40 ). RV: flat with dense radiate striae, regularly spaced. Transapical striae are composed of two macro-areolae, a short and strongly bent macro-areola near the raphe, and a marginal and longer one. In between, externally and internally, a very narrow lunarshape devoid of apparent ornamentation, that can also be absent ( Fig. 43 ). RV striae: 37 in 10 µm ± 2. Raphe filiform and straight. External proximal raphe endings somewhat expanded, distant and coaxial ( Figs 43–44 ). Central area small and rhomboid ( Fig. 44 ). Terminal raphe fissure largely hooked on the mantle ( Fig. 42 ). Helictoglossae small and unraised. RVVC extended (30–50% of the valve, 39 rows of ornamentation in 10 µm), open, with marginal rows of simple pores ( Figs 45–48 ), each row of pores corresponding to a RV stria, ornamentation present up to the edge of the RVVC ( Figs 45, 48 ). Head pole of the RVVC indented (no ‘plow sock’ structure), foot pole of the RVVC with parallel borders from each side of the raphe ( Fig. 46 , arrowheads).

Remarks:—Some differences between Amphicocconeis antiqua and A. clypeus: SV sternum with cupules in A.antiqua , giving it an elliptic shape, while narrow and straight with no ornamentation in A. clypeus. SVVC with large fimbriae in A. antiqua . RV with denser striation in A. antiqua and with a narrower void lunar-shaped space than in A. clypeus. RVVC with a different shape and striation between both taxa and with ornamentation up to its edge in A. antiqua . The SV of A. antiqua is somehow close to that in A. disculoides , but the SVVC are dissimilar within both taxa, and the RVVC is open in A. antiqua . A taxon close to A. antiqua is present in Zimbros (Peninsula do Porto Belo, Santa Catarina, Brazil), and will need further examination (i.e., of the RV and SV in external view) before definitive classification.

Type locality:—Sample ‘Papeete 4 Holothuria ’, Tahiti Nui West coast, Arué District, North of Tombeau du Roi (17◦31.405′S, 149◦31.106′W), collected by scraping a specimen of Holothuria atra , depth 20 cm, by C. Riaux-Gobin, 24 October 2010.

n = SEM observed specimens

Holotype:—Stub 5 18/05/2012, BM001222885. Holotype specimen illustrated in Fig. 35 . Syntypes:—Slides BM101645, Natural History Museum , London , UK, ZU8/38, Hustedt collection, Bremerhaven .

And stub 2 27/04/2012 (Stub made from the sample ‘Papeete 4 Holothuria ’) BM001222886. Specimen illustrated in

Fig. 36 .

Etymology:—The specific epithet antiqua refers to the ogival apices of the frustule, remembering gothic architecture.

Figures

FIGURES 35–40. Amphicocconeis antiqua sp. nov. SEM (material ‘Papeete 4 Holothuria’, from Tahiti, South Pacific). SVs in external view, note the elliptic sternum with cupules (Figs 35, 37, twin arrows), ogival apices and almost no shorter striae (Figs 35–36), SV areolae in external view, with straight and narrow opening and cupules (Figs 37–38), SVVC with simple fimbriae (Fig. 40, arrowhead), SV in internal view, with elliptic large sternum and narrow hymenes (Fig. 38). Scale bars: 6 µm (Fig. 36), 5 µm (Fig. 35), 4 µm (Fig. 39), 3 µm (Figs 38, 40), 1 µm (Fig. 37).

FIGURES 41–44. Amphicocconeis antiqua sp. nov. SEM (material ‘Papeete 4 Holothuria’, from Tahiti, South Pacific). RV in external view, with dense macro-areolae shortly interrupted by narrow spaces devoid of ornamentation or not (Figs 41, 43), terminal raphe strongly hooked (Fig. 42), central area round to slightly transapically expended (Fig. 44). Scale bars: 5 µm (Fig. 43), 4 µm (Fig. 41), 2 µm (Fig. 44), 1 µm (Fig. 42).

FIGURES 45–48. Amphicocconeis antiqua sp. nov. SEM (material ‘Papeete 4 Holothuria’, from Tahiti, South Pacific). RV in internal view with RVVC still in place (abvalvar view) with dense rows of simple pores close to the edge of the copula (Fig. 45), foot pole of the RVVC (abvalvar view) with parallel endings around the raphe and helictoglossa (Fig. 46, twin arrowheads), detached RVVC in advalvar view (Fig. 47), RVVC in abvalvar view with radiate rows of simple pores and narrow edge void of pores (Fig. 48, arrow). Scale bars: 5 µm (Fig. 45), 4 µm (Fig. 47), 2 µm (Figs 46, 48).