Disymmetria reticulata, gen. nov., sp. nov. (Mediophyceae: Thalassiosirales), a new genus in Lauderiaceae emend., and transfer of Lauderia excentrica

Abstract

A discoidal, heteropolar diatom with bilateral valve symmetry is morphologically close to Lauderia excentrica and I propose a new genus, Disymmetria to accommodate them both and restore Lauderia to Hasle’s concept of the genus. The new genus is characterized by a pseudoloculate outer rim with anastomosing costae, valve face divided transversely into a bounded basal dome and a depression with radiating striae separated by costae. In Disymmetria reticulata sp. nov., the valve surface is strongly undulate and the basal dome is also pseudoloculate with numerous fultoportulae, in contrast to D. excentrica, in which the valve face is weakly undulate and only the periphery is pseudoloculate. The new genus also leads to an emended definition of Lauderiaceae to focus on the shared character of valve structure.