Cocconeidacaea Kützing

Al-Handal, Adil Y., Compère, Pierre & Criobe-Usr, Catherine Riaux-Gobin, 2016, Marine benthic diatoms in the coral reefs of Reunion and Rodrigues Islands, West Indian Ocean, Micronesica 2016 (3), pp. 1-78 : 19-20

Family Cocconeidacaea Kützing

Amphicocconeis mascarenica Riaux-Gobin et Compère (Pl. 7, Fig. 2, Pl. 12, Fig. 4) References: Riaux-Gobin et al. 2011a, p.176, figs 1-6 (LM), figs 7-27 (SEM). Riaux-Gobin et al. 2011c, p.18, pl. 1, figs (LM) 8-12, pls. 21, 22, 23, 24, figs (SEM) 1-5.

Features: Apical axis: 9-21 µm, transapical axis: 4.5-8 µm, striae (SV) 12-14 in 10 µm. Valves elliptic with rounded apices. Raphe valve slightly concave, raphe straight and filamentous with slightly inflated central endings, terminal raphe endings deflected to the same direction. SV convex with large sternum and uniseriate striae. Areolae oblong and arranged in a number of regular bands, median areolae larger, marginal areolae slightly denser.

Remarks: A. mascarenica can be compared to A. disculoides (Hustedt) De Stefano et Marino but can be recognized by its oblong shape, more acute apices, and by several other features concerning its RV and RV valvocopula (RVVC) (see detailed remarks in Riaux-Gobin et al. 2011ab, p 178). SV only were observed under LM. Specimens slightly larger than those described by Riaux-Gobin et al. (2011a) with less stria density. Until present, the distribution of this species may confined to tropical regions but according to Riaux-Gobin et al (2011a), the illustration of Cocconeis sp. by Loseva (1992, p. 63, figs 24-27) might pertain to A. mascarenica which expands its distribution to Northern Europe.

Occurrence: Common in Reunion but rare in Rodrigues Island.

Cocconeis alucitae Riaux-Gobin et Compère (Pl. 7, Fig. 1 ) References: Riaux-Gobin et Compère 2008, figs 2-17; Riaux-Gobin et al. 2011c, p. 19, pl. 1, figs 4, 5. pl. 2, figs 1-6 (LM); pl. 27, 1-7 (SEM), pl. 28, figs 1-4 (SEM).

Features: Apical axis: 22-26 µm, transapical axis: 16-20 µm, striae 11-12 in 10 µm on the sternum valve and 29- 22 in 10 µm on the raphe valve. Valves elliptical with round apices. Raphe straight, terminal raphe endings far from poles and very slightly deflected into opposite directions. Striae on RV uniseriate, becoming biseriate near the valve margins. SV convex with uniseriate striae in mid-valve, becoming biseriate and then tri or quadriseriate near the margins.

Remarks: Valve outline relatively similar to C. scutellum Ehrenberg. De Stefano et al. (2008) described C. scutellum var. gorensis , a taxon with features close to those of C. alucitae , except for its SV sternum and raphe that are straight, while slightly oblique in C. alucitae (see remarks in Riaux-Gobin et al. 2011c, p. 20).

Occurrence: Common in Reunion and rare in Rodrigues Island.

Figures

Figure 1. Map showing location of Reunion and Rodrigues Islands, Indian Ocean and sampling sites.