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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.

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

Authority

(Brightw.) Sundström (1986: 99, figs 258–266)

Class

Diatomophyceae

Order

Centrales

Family

Rhizosoleniaceae

Synonyms

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.

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Basionym

Rhizosolenia alata Brightw. (Brightwell, 1858: 96, pl. 5, figs 8, 8a)

Additional References

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)

Description

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).

Distribution

Heard I. and ADBEX; widely distributed in the Antarctic (Jordan et al., 1991); Southern Seas (Hendey, 1937).

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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