Amphicocconeis ruatara Riaux-Gobin, 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 : 49-52

Amphicocconeis ruatara Riaux-Gobin sp. nov. SEM Figs 49–61 . Table 1

Description:— SEM. Valves oblong-elliptic to elongate, with slightly rostrate apices ( Fig. 51 ). Axially bent in cingular view. Valve length 15 ± 2 µm, 14–17 µm. Valve width 6 ± 2 µm, 6–8 µm; L/ W 6.2 ± 0.8; n = 54 (SEM) ( Table 1). SV convex with a concave narrow sternum ( Figs 49–50 ). One row of large and transapically elongated areolae on each part of the sternum, one marginal row of dense and short areolae and, in between these two sectors, short areolae arranged more or less in quincunx. Often a low crest (or crista marginalis) delineating the marginal row of dense and short areolae, as a sort of short mantle ( Figs 49–50 , arrow). SV striae parallel in mid-valve, slightly radiate and denser on apices, uniseriate. SV striae 22 ± 3 in 10 µm. SVVC open, narrow (or sometimes larger), composed of short fused fimbriae (27 in 10 µm), separated from each other by an irregularly biseriate row of pores ( Figs 52–54 ), festooned edge. Head pole of the SVVC with very short fimbriae. RV flat, dense striae composed of one narrow macro-areola, short supplementary marginal striae on mid-valve ( Fig. 55 ). Raphe filiform. Proximal raphe endings externally simple and relatively close to each other, central nodule slightly elevated externally and unique for the genus ( Figs 55–56, 59 ). Terminal raphe endings largely hooked on the mantle ( Fig. 58 ). Raphe sternum somewhat elevated internally, with raphe slit slightly undulating. Proximal raphe endings simple and coaxial internally ( Fig. 57 ). Central area small. RV striae 51 ± 6.5 in 10 µm; 42–60 in 10 µm. RVVC open, 30–50% valve width, 51 rows of uniseriate pores in 10 µm ( Figs 60–61 ).

Holotype:—Stub12 12/02/2020, BM001222887. Holotype specimen illustrated in Fig. 49 .

Syntypes:—Whole slide from the sample RAI 20, deposited at NHM ( BM 81917 material) .

Etymology:—The specific epithet ruatara refers to the Ruatara rock (Raivavae Isl.) on the intertidal coastal environment where was first found the new taxon.

Locality:—Ruatara rock (‘Rocher de l’Homme’), Raivavae (Austral Islands, South

Pacific), RAI 20 and RAI 18 (intertidal red macroalgal turfs on fissures of the rock). Geo localization: S 23° 51.274’; W 147° 39.595’; T°C 23°.7, salinity <40‰. Sampled by C. Riaux-Gobin on 08 October 2018.

Remarks:—Some similarities of A. ruatara sp. nov. with A.discrepans (A.W.F.Schmidt) Riaux-Gobin, Witkowski, Ector & Igersheim ( Riaux-Gobin et al. 2018: figs 15–16), but with some differences: The axial rows of SV areolae on each part of the sternum are larger on A. ruatara than on A. discrepans , along with (in most cases) the presence of a crista marginalis delineating a narrow mantle on the new taxon. The SVVC in A. ruatara has short fused fimbriae with irregularly uni- to biseriate rows of pores, in contrast with a marginal row of one small pore in A. discrepans . The RVVC of A. ruatara shows dense uniseriate rows of pores (51 in 10 µm), while showing one marginal and elongate pore in A. discrepans (30–31 in 10 µm; Riaux-Gobin et al. 2018: figs 17–20).

Figures

FIGURES 49–54. Amphicocconeis ruatara sp. nov.SEM (material RAI 20 from Raivavae,Austral Islands, South Pacific). SV in external view, note the axial rows of long areolae, crista marginalis and marginal row of small and dense areolae (Figs 49–50), SV in internal view (Fig. 51), SVVC in advalvar view with short fused fimbriae (Fig. 52), detail of the SVVC head pole with low fimbriae (Fig. 53), and irregular rows of pores (Fig. 54). Scale bars: 3 µm (Figs 49–52), 1 µm (Figs 53–54).

FIGURES 55–61. Amphicocconeis ruatara sp. nov. (material RAI 20 from Raivavae, Austral Islands, South Pacific). RVs in external view (Figs 55–56), RV in internal view (Fig. 57), detail of the RV apex with terminal raphe fissure (Fig. 58), central area in external view (Fig. 59), head pole of the RVVC in advalvar view (Fig. 61), entire RVVC in advalvar view (Fig. 60). Scale bars: 3 µm (Figs 55–56, 60), 2 µm (Fig. 57), 1 µm (Figs 58–59, 61).