Hust. (Hustedt, 1958: 165, pl. 10, figs 108–112)
Jousé et al. (1962: 86, pl. 3, fig. 8), Kozlova (1962: pl. 9, fig. 10), Hasle (1965b: 26, pl. 9, figs 7–10; pl. 10, fig. 1), Hasle & Syvertsen (1997: 302, pl. 68, tab. 73)
[after Hasle (1965b)] Cells solitary, elliptical to lanceolate in valve view when small, broad and linear with tapering ends when large; apical axis 10–33 µm; transapical axis 8–13 µm. Transapical striae 10–14 in 10 µm. Interstrial membranes perforated by 1 row (2 rows near the margin) of short tube-like poroids, 12–16 in 10 µm. Canal raphe with broad fibulae and narrow apertures between them. Raphe ends with a minute notch.
South Atlantic–Antarctic, 51°29’S 0°08’W to 69°43’S 06°30’E (Hustedt, 1958); Antarctic, BRATEGG (Hasle, 1965b); Lützow-Holm Bay (Tanimura et al., 1990).
While we have not seen this species, F. separanda has been compared with F. rhombica (angulata), probably the most closely related taxon (Hustedt, 1958). In at least some investigations of Southern Ocean planktonic diatoms, F. separanda is likely to have been misidentified as F. rhombica (Hasle, 1965b).
Fragilariopsis separanda, F. rhombica and Nitzschia barbieri are rather similar in gross morphology (see Table). Hustedt (1958) regarded the valve outline of F. rhombica to be predominantly lanceolate to linear, while that of F. separanda was linear. However, illustrations of the two species in Hasle (1965b) show considerable overlap of valve shapes.
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Apical axis (µm)
Striae in 10 µm
Rows of areolae