Ultrastructure and distribution of<i>Aulacoseira gessneri</i>

Abstract

Aulacoseira gessneri (Hustedt) Simonsen has been mentioned rarely in the literature and its ultrastructure has not yet been investigated. The species was originally described from an Amazonian river, and its occurrence is still restricted to Brazilian environments. Specimens, found in Pantanal of Mato Grosso eutrophic lakes, were described and illustrated using optical and electron microscopy, and its morphology compared with similar species, A. distans (Ehrenberg) Simonsen and A. muzzanensis (Meister) Krammer. Aulacoseira gessneri presented the following diacritical characteristics: long filaments joined by small connection spines, elongated separation spines, valve mantle ornamented by straight striae composed of areolae usually round, ringleiste poorly developed, and row of sessile rimoportulae near the collum. The species reached high biomass (11–12 mg L−1) both during the high and low water periods in Pantanal lakes.