Ancyromonas sigmoides Kent 1880

Ancyromonas sigmoides Kent 1880 (Figs 3l–m)

Observation: Gliding flagellate. Cell outline is oval. Cells are 3 to 5 µm long and dorso-ventrally flattened. The cells have a shallow groove ventrally near an anterio-lateral margin of the cell. The cells have a thin stiff anterior flagellum emerging from an anterior depression. The anterior flagellum can be easily overlooked and beats slowly. The posterior flagellum is about 1.5 times the cell length and may not be acronematic. The cells move by gliding with the posterior flagellum trailing. Commonly observed.

Remarks: Previously reported lengths range from 2 to 7.6 µm. This species has been reported from marine sites in Antarctica, Australia, Arctic Canada, Denmark, Fiji, Gulf of Finland, Greenland, Hawaii, Eastern Pacific (hydrothermal vent) and Panama (Larsen and Patterson 1990; Vørs 1992a, b; Ekebom et al. 1996; Tong 1997a; Tong et al. 1997; Tong et al. 1998; Atkins et al. 2000; Bernard et al. 2000). The observations are in agreement with those of previous authors. Ancyromonas sigmoides can be confused with Metopion fluens, but is distinguished by the anteriorly directed flagellum; the second flagellum in M. fluens is thicker and directed to the rear. It is similar to A. melba Patterson and Simpson 1996, found in hypersaline habitats of Shark Bay, subtropical Australia, but A. melba has an anterior flagellum which is as thick as the posterior flagellum, and the cell is slightly larger. Three cells had an anterior flagellum, which was basally thickened and the cells were included here (Fig. 3m) and these maybe refer to Ancyromonas micra. Further studies are needed to establish the identity of A. melba, A. micra and A. sigmoides. Ancyromonas sigmoides can be distinguished from Ancyromonas sinistra by the laterally flattened body and its cell shape (A. sinistra is spherical) and from Ancyromonas impluvium by its cell shape. Ancyromonas sinistra has a rugose flange on the left anterior-lateral margin of the cell and Ancyromonas impluvium has an anterior flagellum, which beats more actively.