Plagiogrammaceae De Toni

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 : 6

Family Plagiogrammaceae De Toni

Dimeregramma cf. minor (Gregory) Ralfs ex Pritchard (Pl. 4, Figs 8-10) References: Hustedt 1931 -59, p. 118, fig. 640; Witkowski et al. 2000, p. 29, pl. 11, figs 3-9. Features: Apical axis 16-30 µm, transapical axis: 5-11, striae 16-18 in 10 µm. Cells rectangular in girdle view with convex margins, normally united by valve face to form ribbon-like chains. Valves lanceolate with rounded apices which possess haline areaes. Sternum lanceolate. Striae radiate, particularly towards valve poles.

Remarks: The specimens observed in the Mascarenes match illustrations given by both references mentioned above but the striae density is much higher than those reported. Husted gave striae 9-10 in 10. Further investigation may be required to reveal correct identity of this taxon.

Occurrence: Frequent in Reunion and Rodrigues samples. D. minor var. nana was reported from Seychelles (G).

Plagiogramma staurophorum (Gregory) Heiberg (Pl. 4, Figs 6) References: Hustedt 1931 -59, p. 106, fig. 635; Witkowski et al. 2000, p. 39, pl. 11, figs 16-21, Lobban et al. 2012, p. 254, pl.10, figs 3-5.

Features: Apical axis: 15-35 µm, transapical axis: 5-12, striae 9-11 in 10 µm, areolae 8-9 in 10 µm. Valves linear-elliptic with obtusely rounded apices. Striae radiate and crossed by longitudinal ribs. Remarks: Witkowski et al. (2000) mentioned that valves of this species have parallel margins but the figures they provided (figs 17-21) are all showing elliptic valves where margins are not parallel. Occurrence: Common in Reunion and rare in Rodrigues samples. Previously reported from Seychelles (G).