Morphology, ecology and biogeography of **Stauroneis pachycephala** PT Cleve (Bacillariophyta) and its transfer to the genus **Envekadea**Morphology, ecology and biogeography of **Stauroneis pachycephala** PT Cleve (Bacillariophyta) and its transfer to the genus **Envekadea**
Faculty of Sciences. Biology
Diatom research / International Society for Diatom Research. - Bristol
29(2014):4, p. 455-464
University of Antwerp
Stauroneis pachycephala was described in 1881 from the Baakens River, Port Elizabeth, South Africa. Recently, it was found during surveys of the MacKenzie River (Victoria, Australia), the Florida Everglades (USA) and coastal marshes of Louisiana (USA). The morphology, ecology and geographic distribution of this species are described in this article. This naviculoid species is characterised by lanceolate valves with a gibbous centre, a sigmoid raphe, an axial area narrowing toward the valve ends, and capitate valve apices. The central area is a distinct stauros that is slightly widened near the valve margin. The raphe is straight and filiform, and the terminal raphe fissures are strongly deflected in opposite directions. Striae are fine and radiate in the middle of the valve, becoming parallel and eventually convergent toward the valve ends. The external surface of the valves and copulae is smooth and lacks ornamentation. We also examined the type material of S. pachycephala. Our observations show this species has morphological characteristics that fit within the genus Envekadea. Therefore, the transfer of S. pachycephala to Envekadea is proposed and a lectotype is designated.