Planothidium bilensis sp. nov. (Bacillariophyta) from a Pond in Kiev Megalopolis (Ukraine)*

摘要

Planothidium bilensis sp. nov. has an unusual contacting flap with two lensoids located opposite from each other, and a diagonal position of the sternum. Both lensoids contain one siliceous lenticular db-element and a lenticular cavity next to it, which form a double lens optical system. The main types as well as other different types of lensoids are discussed in the current paper. For the morphological description of the shell of Bacillariophyta, new terms were introduced - plain-convex lensoid (pc-lensoid) and biconvex lensoid (bc-lensoid). The morphology of lensoids corresponds to the species rank taxonomy and can serve as a reliable indicator for differentiation of closely related species. A new species was found in a nameless small pond in the"Zhukov Island" landscape reserve, located in the left bank of the Dnepr River floodplain, in the southern border of Kiev.