(O.F.Müll.) Nitzsch (1817: 4)
Cercaria tripos O.F.Müll. (Müller, 1776: 206)
Lebour (1925: 148, pl. 32, 33), Schiller (1937: 382, figs 384, 385), Sournia (1967: 406, fig. 27), Dodge (1982: 234, fig. 30A–D), Steidinger & Tangen (1997: 478, pl. 26)
Cells 70–90 µm long overall, 50 µm diameter, with a sharp transition from the triangular epitheca to the 60–90 µm long apical horn. Hypotheca rounded to flattened at the antapex, tapering longitudinally into curved antapical horns; antapical horns 50–70 µm long, the left usually longer than the right. Cingulum sometimes reduced to a line, sometimes slightly excavated or with narrow lists. Sulcus a large aperture on the ventral side, extending into the epitheca. Surface ornamentation variable, smooth or reticulate, and with scattered pores, spines or horns.
Southern Ocean, 44–61°S, south of Australia.
A distinctive, armoured genus with long, apical and antapical horns, a prominent cingulum, clear tabulation and longitudinal ribs (Jörgensen, 1911). Tabulation of Ceratium is typically 4', 7'', 6c, 12s, 6''', 1p, 1''''. The central body is sometimes dorsally compressed and chloroplasts are present, although some species have food vacuoles due to phagocytic activity. Only a few taxa have been collected from Antarctic waters, the most prominent being the C. pentagonum/C. lineatum complex and the C. extensum/C. fusus complex.