Hasle, Syvertsen & Medlin (1994: 261, figs 93–110, 142e, tab. 2)
[after Hasle et al. (1994)] Cells solitary; apical axis 16–77 µm; transapical axis 4–5.5 µm. Valves narrowly elliptical; larger cells slightly dilated in central part. Transapical striae parallel, 18–22 (occasionally 14–16) in 10 µm, uniseriate; areolae poroid, 30–40 in 10 µm. Sternum variable, narrow to broad. Apical fields of 5–8 longitudinal slits through the valve wall at one end and 4–7 slits at the other, asymmetrically located on the valve. Labiate process solitary, close to the latter valve end.
Type locality, Antarctic sea-ice, 60°42’S 46°36’W [IMBB Sample 58(12)] (Hasle et al., 1994).
This diatom was not found in the present study. Another Antarctic variety, S. lata var. angustata Hasle, Syvertsen & Medlin, has a more elongate valve outline, although the size ranges overlap (Hasle et al., 1994). Var. angustata also has fewer apical field slits at the labiate process end. Synedropsis lata is distinctive in having a narrowly elliptical to linear valve outline, as well as asymmetrical apical fields with an unequal number of slits at each apex.
Some species formerly included in Fragilaria and Synedra have been transferred to Synedropsis on the basis of their valve striation, the occurrence and structure of labiate processes and apical pore (slit) fields and the nature of the girdle (Hasle et al., 1994). Synedropsis hyperboreoides and S. laevis were collected in the present study, and several other species, e.g. S. fragilis, S. recta, S. lata var. lata and S. lata var. angustata, have been described from Antarctic locations (Hasle, 1994).