Morphology of Biddulphia seychellensis (Grunow in Van Heurck) F.W. Mills and the generic limits of Biddulphia Gray

Abstract

In this paper presented are the res ults of light and e lectron microscopie studies on a marine diatom species Biddulphia seychellensis. The species turned out to be abundant in some samples from the west coast of South Africa and from the western Indian Ocean coral reefs ofScattered Islands (Eparses). Unlike most representatives of the genus, B. seychellensis forms tripolar to square valves, but smallest specimens can be almost circular. The species shares a few features with the generitype, e.g., pseudocelli, few rimoportulae, areolae occluded with cribra and occas ional simple pores. Unlike in the generitype, however, the valve face in B. seychellensis is always flat, pseudocelli indistinct and never raised above the valve level, valvocopula is open, and the marg inal ridge is miss ing. Biddulphia seychellensis has been abundantly observed in warm oceanic waters with somewhat increased salini ty. In addition data on the di stribution in marine littoral are provided.