(Hasle) Hasle (1993: 317)
Fragilaria nana Steem.Neils., in Holmes (1956: fig. 17a, pro parte), Paasche (1961: 201, pl. 1a, fig. 1a), Hasle (1964: pl. 3, fig. 2) See Hasle (1965b) for full synonymy, LM and EM descriptions and discussion of nomenclatural problems.
Nitzschia pseudonana Hasle (1974: 427), Hasle & Medlin (1990c: 181, pl. 24.1, figs 7–14; pl. 24.2, figs 20, 21; pl. 24.8, figs 1–3)
Hasle (1965b: 22: pl. 1, figs 7–14; pl. 4, figs 20, 21; pl. 8, figs 1–9; pl. 17, fig. 6), Moisan & Fryxell (1993: 493), Kang & Lee (1995: 260, fig. 6C), Hasle & Syvertsen (1997: 300, pl. 67)
Cells solitary or in short chains with cells attached by valve faces, elliptical to lanceolate in valve view; larger valves with slightly elongated ends; apical axis 4–20 µm; transapical axis 2.5–5 µm. Transapical striae straight in the middle of the cell, curved near the valve poles, 18–28 in 10 µm. Canal raphe markedly eccentric (Fig. b). Fibulae present in the same number as striae, arcuate, fastened to valve near striae and valve mantle; no indication of a greater distance between the 2 fibulae in the middle. Interstrial membranes perforated by 2 rows of minute areolae, 6–8 in 10 µm, situated close to striae. Outer canal wall without areolae. Pseudonodulus absent; terminal nodules present.
Southern Ocean, south of Australia; Drygalski Glacier, Ross Sea; BRATEGG sample, brownish undersurface of pack-ice, 62°30’S, 19°42’W (Hasle, 1965); KERFIX, 50°40’S 68°25’E, Southern Ocean (Kopczyńska et al., 1998); Bransfield Strait (Kang & Lee, 1995); Weddell-Scotia Confluence (Garrison et al., 1987).
Fragilariopsis pseudonana is also known from cold northern waters (Denmark Strait, 62°N 33°W and 60°18’N 31°00’W; Shetland Is., 61°08.5’N 02°21’W) as well as warmer regions (Gulf of California, Gulf of Panama, Wellington Harbour; Hasle, 1965b). Due to the similarity of cell shape and striation, it is difficult to separate F. pseudonana from small specimens of F. cylindrus. See discussion under F. cylindrus. Generally, Fragilariopsis pseudonana cells are elliptical-lanceolate -valved, whereas (small specimens of ) Fragilariopsis cylindrus are linear-valved.