Habit, frustule morphology and distribution of the antarctic marine benthic diatom Entopyla australis var. gigantea (Greville) Fricke (Entopylaceae)

Abstract

The Antarctic marine benthic diatom Entopyla australis var. gigantea (Grev.) Fricke was collected as an epiphyte on red algae at Anvers Island, Antarctica. Cells of E. australis var. gigantea form ribbon-shaped colonies, and the sibling cells are attached by means of mucilage extruded through the apical pore fields of concave valves. No interlocking marginal spines were found in this SEM study. The cingulum is composed of a series of many open bands with elaborations of ligulae (described as rudimentary septa in the literature) at the poles. Each band has a single row of slits at the advalvar margin of the pars interior. The heterovalvate frustule is flexed in girdle view. Valves have simple multiseriate striae arranged alternately on the two sides of the zigzag sternum, but pronounced marginal ridges are seen only in the convex valve. Concave valves have prominent apical pore fields, whereas the convex valves do not. Rimportulae present on both the valves follow the “one per pole” pattern, but differ in structure and orientation of slits on each valve. On the basis of material from Greville's original collection, we designate the lectotype (BM 10265) in this study and confirm our identification of Antarctic specimens. E. australis var. gigantea appears to have continued from the late Oligocene-early Miocene to the present, with its possible centre of distribution on the eastern Pacific coasts.