Family: Rhizosoleniaceae De Toni
Genus: Proboscia Sundström
Scientific name: Proboscia alata (Brightwell) Sundström
The generic type, Proboscia alata, was first described as Rhizosolenia alata with a series of forms, all with valve extended into a shorter or longer tube with truncate tip (proboscis), and no internal processes. Chain formation by the proboscis of neighboring cells fitting into the claspers on the adjacent valve. Auxospores, formed terminally. The different forms are now regarded as separate species (Throndsen et al., 2007).
Rhizosolenia alata Brightwell
Pavillard, 1925: p. 26, Fig. 38 (as Rhizosolenia alata); Hustedt,1930: p. 599, Fig. 344 (as Rhizosolenia alata); Allen and Cupp,1935: p. 130, Fig. 43 (as Rhizosolenia alata); Cupp, 1943: p. 91,Fig. 52 A (as Rhizosolenia alata); Crosby and Wood, 1958: p.520, Pl. 38: 62 a (as Rhizosolenia alata); Hendey, 1964: p. 146,Pl. II: 2 (as Rhizosolenia alata f. alata); Simonsen, 1974: p. 28 (as Rhizosolenia alata); Priddle and Fryxell, 1985: p. 76-77;Ricard, 1987: p. 171, Figs. 202-205 (as Rhizosolenia alata f. alata); Throndsen et al., 2007: p. 157.
Cells rod-shaped, cylindrical, straight; 7-18 µm in diameter, up to 1 mm in length. Valve shortly conical ending in tubelike, more or less curved oblique process. Depression at base of tube into which apex of adjoining cell fits. Intercalary bands scalelike, rhombic, in two dorsoventrally rows. Cell wall thin, weakly siliceous; finely striated. On valve 21-23 puncta in 10 µm. None observed on intercalary bands. Chromatophores are numerous, small. Auxospores and resting spores, known. Auxospores growing out in the same plane as the main cell (Cupp, 1943).
Cells length 380-550 µm; diameter 17-20 µm.
Oceanic, but often near the coast, temperate species.
Sites of occurrence in RSA:
In Winter 2006 Cruise, this species was frequently observed, often in large numbers at various sites (refer sites map); maximum abundance (5.6*10^3cells/l) was associated with the Sea of Oman (St. 25a). It has been previously reported (as Rhizosolenia alata) from the inner RSA (Simonsen, 1974) and from Kuwaiti waters of the inner RSA (Al-Yamani et al., 2004; AlKandari et al., 2009).