Balech (1973: 10, pl. 1, figs 18–20; pl. 2, figs 21–26)
Balech (1976: 36, fig. 24)
Cells medium-sized, rounded to ellipsoidal, 35–45 µm long, 35–45 µm diameter. Epitheca rounded, well developed, comprising up to 20% of the cell length. Cingulum not incised. Sulcal lists narrow, inconspicuous by LM. Cell surface densely covered with pores; apical and antapical excrescences absent.
Infrequent throughout the Southern Ocean; Antarctic (Balech, 1976).
Dinophysis is a distinctive genus with up to ten representatives in the Southern Ocean. While diversity is lower than in many other marine environments, occasionally species of Dinophysis have been observed to dominate Southern Ocean dinoflagellate floras (Dodge & Priddle, 1987).The genus is characterised by a small rounded to flat epitheca and a much larger, rounded to elliptical hypotheca. The cingulum is well defined and bordered by prominent lists. Lists are also associated with the sulcus which, because of the lenticular shape of the cell, are usually located on the side.Many authors consider Phalacroma to be synonymous with Dinophysis (e.g. Tai & Skogsberg, 1934; Abé, 1967). The genera overlap in many aspects of their morphology, but can be separated the distinctive, funnel-shaped, anterior cingular list of Dinophysis. Other features, such as the development and direction of cingular lists in combination with the height and shape of the epitheca, also help to distinguish the genera. Members of the genus Dinophysis are specialised predators, and Hansen (1991) observed D. rotundata Clap. & J.Lachm. (= Phalacroma rotundatum ) and D. hastata Stein ingesting the prostomatid ciliate Tiarina fusus (Clap. & J.Lachm.) Bergh.
Dinophysis tenuivelata can be distinguished from D. contracta by its larger size, smaller and rounded (as opposed to conical) epitheca and non-incised cingulum. There can be difficulty in separating D. tenuivelata from Phalacroma rotundatum (q.v.), but the latter is usually more ellipsoidal and has a somewhat flattened epitheca.