Ultrastructure of Aulacoseira brasiliensis sp. nov. (Coscinodiscophyceae) and comparison with related species.

Abstract

This paper describes and illustrates Aulacoseira brasiliensis Tremarin, Torgan et T. Ludwig sp. nov. under light and electron microscopy and compares their ultrastructure with similar species obtained from Hustedt's collection samples. The new species is characterized by forming short chains linked by ovate-attenuate spines, rounded areolae occluded by vola, undeveloped ringleist and sessile rimoportulae arranged in two circumferential alternate rows. The spines shape, rimoportulae disposition, valve surface and mantle areolation pattern are very particular. The ultrastructural features of the frustules of A. brasiliensis are compared with those of A. muzzanensis, A. agassizii var. agassizzi and A. agassizii var. malayensis, particularly with respect to the areolation pattern, position, number and shape of rimoportulae. A. brasiliensis was found in lotic and lentic environments of tropical and subtropical regions from Brazil.