(N.Peters) Balech (1967: 82)
Phalacroma cornuta N.Peters (1928: 20, fig. 1)
Phalacroma spinata N.Peters (1928: 22, fig. 2)
Balech (1976: 33, fig. 21)
[after Balech (1976)] Cells medium-sized with an irregular rounded to triangular outline, 45–64 µm long, 40–50 µm diameter. Epitheca large, rounded. Excrescences well developed and irregular at apex and antapex. Left sulcal list wide, flared at the base (at R3). The 2 upper sulcal rays (R1 and R2) close together. Cingulum moderately indented. Cell surface covered with pores. Chloroplasts present.
Southern Ocean, near South Georgia (Dodge & Priddle, 1987); confined to south of the Polar Front (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.
This uncommon but distinctive species was not seen by us. Balech (1976) recognised subsp. cornuta and subsp. inerme Balech (in Balech & El-Sayed, 1965: 115, pl. 1, figs 12-18), based on the development of excresences. The latter lacks apical excrescences and has only inconspicuous antapical excrescences. The tubular outgrowths usually present in the dorsal and antapical sagittal regions of D. norvegica Clap. & J.Lachm. from Northern Hemisphere waters are similar to those of D. cornuta (Taylor & Pollingher, 1987). Dinophysis cornuta is relatively easy to identify because of its irregular outline caused by pronounced apical and antapical excrescences and by its extended left sulcal list.