Metopion fluens Larsen and Patterson 1990 (Fig. 4d)

Observation: Cells are ovate, 4 to 9 µm long, laterally compressed and with a small rostrum anterior to the flagellar insertion. Small bodies are seen in the protrusion or at the proximal anterior part of the cell. Two flagella of unequal size emerge from a ventral groove located in the left side of the cell. The thickened long flagellum is about 1.5 times the cell length and is not tapered at the tip, and the shorter flagellum may be difficult to see. The nucleus is situated near the groove. The cells move by gliding. Rarely observed.

Remarks: This species has been found in marine sites in the world (Lee and Patterson 1998; Al-Qassab et al. 2002; Lee 2002b, 2006), with cell length of 3 to 9 µm. The observations are in accord with those of previous authors. This species is similar to Ancyromonas sigmoides, but is distinguished by its broad anterior end and by the position of the second flagellum – that of M. fluens is directed posteriorly, while that of Ancyromonas sigmoides is directed anteriorly.