(Schütt) Balech (1967b: 83)
Phalacroma operculoides Schütt (1895, pl. 2)
Balech (1988: 49, pl. 10, figs 11–15)
Cells medium-sized, rounded, 40–62 µm long, c. 40 µm diameter. Epitheca very reduced, flat to slightly rounded. Cingulum 7 µm wide, not incised; anterior cingular list wider (4 µm) than posterior list, both lists smooth and projected anteriorly. Sulcal lists smooth; left sulcal list extending for half cell length, c. 8 µm wide, with 3 visible rays; right sulcal list c. half length of and narrower than the left list. Cell surface comparatively smooth, with scattered pores. Chloroplasts present.
Southern Ocean, south of Australia, 44–60°S; South Atlantic (Balech, 1988); South Georgia (Dodge & Priddle, 1987).
CommentsDinophysis 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.