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

Authority

(O’Meara) Hust. (Hustedt, 1952: 296, figs 6, 7)

Class

Diatomophyceae

Order

Pennales

Family

Bacillariaceae

Synonyms

Fragilaria rhombica (O’Meara) Heiden & Kolbe (1928: 552, pl. 6, figs 129, 130)
Nitzschia antarctica Okuno (1954: 24, pl. 3, fig. 7)
Nitzschia angulata Hasle (1972a: 115)

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Basionym

Diatoma rhombicum O’Meara (1877: 22, pl. 1, fig. 2)

Additional References

Hustedt (1958: 163, figs 113–120), Hasle (1965b: 24, pl. 1, fig. 6; pl. 4, fig. 19; pl. 6, fig. 5; pl. 8, fig. 11; pl. 9, figs 1–6; pl. 10, figs 2–6), Hasle & Medlin (1990c: 181, pl. 24.1, fig. 6; pl. 24.4, figs 1–6), Moisan & Fryxell (1993: 493), Hasle & Syvertsen (1997: 300, pl. 68, tab. 73)

Description

Cells circular to elliptical, pointed towards the poles; apical axis 8–53 µm; transapical axis 7–13 µm. Transapical striae straight in the centre, curved towards the poles, 8–16 in 10 µm, somewhat thickened internally (Fig. c). Interstrial membranes comprising (1 or) 2 rows of poroid areolae; areolae 22–26 in 10 µm. Fibulae 8–16 in 10 µm. Central nodule absent.

Distribution

Coastal waters near Davis Station, East Antarctica; Terra Nova Bay; Southern Ocean, 57°35’S 105°46’E, offshore Wilkes Land; Weddell-Scotia Confluence (Garrison et al., 1987); BRATEGG Antarctic samples (Hasle, 1965b); Heard I. (Manguin, 1954); Indian Ocean sector of the Antarctic (Jousé et al., 1962; Kozlova, 1962); Bellingshausen Sea and South Orkneys (Frenguelli & Orlando, 1958).

Comments

Fragilariopsis rhombica, F. separanda 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.

Table: Comparison of Fragilariopsis rhombica, F. separanda and Nitzschia barbieri (data from Hasle & Medlin, 1990c).

Apical axis (µm)

Striae in 10 µm

Rows of areolae

F. rhombica

8–53

8–16

1–2

F. separanda

10–33

10–14

1

N. barbieri

49–118

8–11

1 (–2)

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