(Brightw.) Sundström (1986: 99, figs 258–266)
Rhizosolenia alata f. genuina Gran (1908: 56, fig. 68b, c), nom. inval.Rhizosolenia obtusa auct. non Hensen (1887), sensu Ostenfeld (1908: 56, fig. 69)See Jordan et al. (1991) for full synonymy.
Rhizosolenia alata Brightw. (Brightwell, 1858: 96, pl. 5, figs 8, 8a)
Hustedt (1927–30: 600, fig. 344), Hendey (1937: 310), Manguin (1960: 264, pl. 26, fig. 318), Hendey (1964: 146, pl. 2, fig. 2), Priddle & Fryxell (1985: 76, figs A, B), Ferreyra & Ferrario (1983a: 1, pl. 1, 2), Jordan et al. (1991: 65, figs 1–9), Hasle & Syvertsen (1997: 159, pl. 30)
Cells solitary or in short chains of c. 4 cells, long, cylindrical; apical axis 2.5–13 µm. Valves subconical, asymmetrical, tapering to an eccentric slightly curved proboscis; proboscis tip truncate, bearing a short longitudinal slit, a terminal ring of fine spinules and another small groove; contiguous area developed as a groove into which distal end of sister cell links; claspers unequal, slightly protruding. Valve areolae fine, poroid, on basal part of valve. Girdle bands in 2 dorsiventral columns, with pores and loculate areolae. Auxospores terminal in chain (Hasle & Syvertsen, 1997). Chloroplasts almost certainly discoid (Round et al., 1990).
Heard I. and ADBEX; widely distributed in the Antarctic (Jordan et al., 1991); Southern Seas (Hendey, 1937).
Five species are currently recognised (see discussion in Hasle & Syvertsen, 1997), although further EM investigations may see taxa of the closely related Rhizosolenia being transferred to Proboscia. Three species have been reported from Antarctic waters, P. alata, P. inermis and P. truncata (Jordan et al., 1991). In the same publication, the authors identified ‘winter’ and ‘spring’ forms of these diatoms, noting that winter forms have a longer proboscis.