Ultrastructure of Delicata sinensis Krammer et Metzeltin and D. williamsii sp. nov. (Bacillariophyta) from China

Abstract

Two sympatric species, Delicata sinensis Krammer et Metzeltin and D. williamsii sp. nov. are studied under light and scanning electron microscopy. Both species possess open valvocopulae, which is reported for the first time within the genus. Delicata sinensis often exhibits a semifascia-like central area but sometimes only a little broadened central area bordered by a few shortened striae in the middle part of the dorsal side. Regarding D. williamsii, a freshwater, epilithic taxon, it exhibits a unique combination of characters: a dorsiventral valve outline, non-produced ends and, remarkably, widely spaced 2-3 very long striae in the middle part of the dorsal side. Its status as a distinct species can be confirmed by the presence of 3-4 stigmata on the central area of the ventral side and the undulated striae, more distinctly near the pole. Delicata williamsii is finally compared morphologically with similar Delicata species