(Claparède and Lachmann, 1859)
Body fusiform, tapering posteriorly, sometimes with short spines, anteriorly toothed. Cytostome apical, invaginated. Five transverse rows of rectangular, calcareous plates with lateral teeth in cortex. One macronucleus, 1 micronucleus. About 15 longitudinal somatic kineties between plates; 1 elongate caudal cilium. Dorsal brush composed of 3 short dikinetidal rows slightly oblique to main body axis. Swims rapidly in sinusoid trajectory. Size in vivo 85-135 x 22-45 µm. May comprise several species (Kahl, 1930). Mass occurrences may cause red tides (Dale and Dahl, 1987b).
Ref.: Hamburger and Buddenbrock (1911), Fauré-Fremiet (1924), Kahl (1930), Small and Lynn (1985).