Morphology, ecology and biogeogra phy of Stauroneis pachycephala P.T. Cleve (Bacillariophyta) and its transfer to the genus Envekadea

Stauroneis pachycephala was describ ed in 1881 from the Baakens River, Port Elizabe th, South Africa. Recently, it was found during surveys of the MacKenzie River (Victoria, Australia).The morphology, ecology and geographic distribution of this species are described in th e present paper. This naviculoid species is characterised by lanceolate valves with a gibbous centre, a sigmoid raphe, an axial area narro wing 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. Stria e 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. W e also examined the type material of S. pachycephala. The observations show this species has morphological character istics that fit within the genus Envekadea. Therefore, the transfer of S. pachycephala to Envekadea is proposed and a lectot ype is designated.

Stauroneis pachycephala was describ ed in 1881 from the Baakens River, Port Elizabe th, South Africa. Recently, it was found during surveys of the MacKenzie River (Victoria, Australia).The morphology, ecology and geographic distribution of this species are described in th e present paper. This naviculoid species is characterised by lanceolate valves with a gibbous centre, a sigmoid raphe, an axial area narro wing 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. Stria e 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. W e also examined the type material of S. pachycephala. The observations show this species has morphological character istics that fit within the genus Envekadea. Therefore, the transfer of S. pachycephala to Envekadea is proposed and a lectot ype is designated.