Cocconeis borbonica Riaux-Gobin

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 : 20

Cocconeis borbonica Riaux-Gobin et Compѐre (Pl. 12, Fig. 6) References: Riaux-Gobin & Compѐre 2008, Figs 24-32 (SEM), 45-47 (LM).

Features: Apical axis: 10-15 µm, transapical axis: 4-5 µm, striae (SV) 40-50 in 10 µm. Valves oblong with round apices. Raphe straight, proximal raphe endings close to each other, terminal raphe endings enlarged and slightly deflected to opposite directions. Striae irregularly spaced on the RV. On SV, striae arranged regularly and appear in 4-5 apical rows.

Remarks: Very small species which can hardly be distinguished under LM. Differs from Cocconeis finmarchica Grunow by a denser striation on both valves and reduced dimensions. Also differs from C. oblongata Edsbagge and some other taxa (see Riaux-Gobin et al. 2008). We can note that Car et al. (2012) described a taxon very similar to C. borbonica , with very slight differences possibly due to plasticity of the taxon, under Cocconeis caulerpacola Witkowski, Car et Dobosz. Marine to brackish water species.

Occurrence: So far only recorded from Reunion Island. Frequent.

Cocconeis convexa Giffen (Pl. 7, Fig. 5) References: Witkowski et al. 2000, p. 104, pl. 37, figs 5, 6, pl. 41, figs 1-4; Riaux-Gobin et al. 2011c, p. 22, pl. 3, figs (LM) 1-5, pl. 32, figs (SEM) 1-7.

Features: Apical axis: 18-20 µm, transapical axis: 13-18 µm, striae on raphe valve 24-26 in µm. Valves broadly elliptic with round apices. Raphe valve concave, raphe straight, distal raphe endings elongate. SV convex, sternum narrow.

Remarks: This is a widely distributed species in tropical to temperate littoral regions. Also found in inland waters characterized by high conductivity ( Al-Handal 2009).