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Ocean Ecosystems/ESRIG, University of Groningen and Arctic Centre, University of Groningen and the RaTS program, British Antarctic Survey.

Ocean Ecosystems/ESRIG, University of Groningen and Arctic Centre, University of Groningen and the RaTS program, British Antarctic Survey.

Authority

(Castrac.) R.W.Jord. & Ligowski, in Jordan et al. (1991: 66, figs 10–18)

Class

Diatomophyceae

Order

Centrales

Family

Rhizosoleniaceae

Synonyms

Rhizosolenia obtusa auct. non Hensen (1887), sensu Hardy & Gunther (1935: 53, fig. 23)
Rhizosolenia inermis f. castracanei Heiden & Kolbe (1928: 521)
Proboscia alata f. inermis (Castrac.) Hust. (Hustedt, 1927–30: 602, fig. 348), sensu Hendey (1937: 311, “inermis” phase)
Proboscia (ex Rhizosolenia) “alatasensu Mullins & Priddle (1987: 57, 59)

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Basionym

Rhizosolenia inermis Castrac. (Castracane, 1886: 71, pl. 24, figs 7, 8, [10], 13), De Toni (1894: 830)

Additional References

Cupp (1943: 90, fig. 52E), Ferreyra & Ferrario (1983a, pl. 1, figs 6, 13), Priddle & Fryxell (1985: 76, figs C, D, M, as R. alata), Priddle et al. (1990: 119, pl. 15.3, figs 6a, b, as R. inermis), Moisan & Fryxell (1993: 293)

Description

Cells solitary or often in chains to 1 mm long, cylindrical; apical axis 10–19 µm. Valves conical, tapering to a stout proboscis; proboscis slightly expanded, with a short longitudinal slit just below the tip which is surrounded by a ring of fine spinules (Fig. b); contiguous area developed as a groove (Fig. b,d); claspers equal, protruding distally. Girdle bands in 2 dorsiventral columns.

Distribution

Originally described from Antarctic waters (Castracane, 1886); Antarctic (Priddle et al., 1990).

Comments

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.

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