(Ehrenb.) N.E.Br. (Brown, 1920: 232)
Cocconeis pacifica Grunow (1867: 11, pl. 1, fig. 10)Cocconeis imperatrix A.W.F.Schmidt (1894: pl. 189, figs 3, 10, 15)Cocconeis costata var. pacifica (Grunow) Cleve (1895: 182)Cocconeis pinnata var. plena Perag. (Peragallo, 1921: 53, pl. 2, fig. 4)Cocconeis imperatrix f. plena (Perag.) Freng. (Frenguelli, 1943: 230, pl. 1, figs 3, 4)
Rhaphoneis fasciolata Ehrenb. (Ehrenberg, 1844b: 204; 1854: pl. 35A/22, fig. 16)
Peragallo (1921: 51, as C. costata var. pacifica), Andreoli et al. (1995: 472, fig. 9), Everitt & Thomas (1986: 8, fig. 3F)
Cells solitary, elliptical; apical axis 15–160 µm; transapical axis 25–75 µm. Transapical striae radiating, composed of poroid areolae arranged in alternating alveolus-like structures (Fig. d). Raphe-valve slightly concave; R-valve transapical striae 4–6 in 10 µm near the margin, 5–7 in 10 µm near the centre; interstrial costae broad, slightly raised. Raphe a simple fissure of ±parallel sides with central endings (external) slightly dilated, but internally constricted where they diverge towards valve margin. Pseudoraphe-valve convex, with a narrow straight pseudoraphe (Fig. b); P-valve costae 3–4 in 10 µm near the margin, 5–6 in 10 µm near the centre.
Ellis Fjord, Plough I. and coastal waters near Davis Station, East Antarctica (Everitt & Thomas, 1986); Booth-Wandel I., Cape Tuxen, Petermann I. and Port Lockroy (all Antarctic Peninsula) (Peragallo, 1921).
Cocconeis cells are solitary and heterovalvate. One valve (the P-valve) is typically convex and bears a pseudoraphe; the other (the R-valve) is concave (or at least less convex than the P-valve) and bears a central raphe-sternum. Valve structure is usually of broad, non-areolate, transapical costae alternating with striae (intercostal areas) that contain uniseriate or multiseriate poroids (areolae). The arrangement of striae and costae on the P-valve often differs from that on the R-valve.