Actinocyclus curvatulus Janisch

Division: Chromophyta
Class: Bacillariophyceae
Order: Biddulphiales
Suborder: Coscinodiscineae
Family: Hemidiscaceae Hendey
Genus: Actinocyclus Ehrenberg
Scientific name: Actinocyclus curvatulus Janisch

Genus is characterized by more or less distinct fasciculated areolation (areola rows in sectors); more or less distinct marginal zone different from the rest of the valve; distinct central annulus and pseudonodulus at or near the valve margin. Many small chloroplasts are present (Throndsen et al., 2007).

Synonym:
Coscinodiscus curvatulus var. subocellata Grunow

References:
Pavillard, 1925: p. 14, Fig. 19 (as Coscinodiscus curvatulus); Hustedt,1930: p. 538, Fig. 307; Cupp, 1943: p.55, Fig. 17, Pl. 1: 2 (as Coscinodiscus curvatulus); Hendey, 1964: p. 81 (as Coscinodiscus curvatulus); Simonsen,1974: p. 20; Priddle and Fryxell, 1985:p. 106-107; Witkowski et al., 2000: p.20, Pl. 6: 2; Throndsen et al., 2007: p.147.

Description:
Central annulus irregular in outline. Areola rows are slightly curved and parallel to the side row of the sectors. Labiate processes at the end of side rows. Pseudonodulus small and close to the mantle. Diameter 13-160 µm; 8-18 areolae in 10 µm; 7-9 µm between the marginal processes(Throndsen et al., 2007).

Dimensions:
Valve diameter 35-42 µm.

Distribution:
Cosmopolitan species.

Sites of occurrence in RSA:
In Winter 2006 Cruise, this species occurred at various sites (refer sites map), usually in small numbers; maximum abundance (1.2*10^2 cells/l) was observed in the waters of the Sea of Oman (St. 95). It has been previously reported from the inner RSA (Simonsen, 1974).