(®gures 20g, 21d, e)
Description. Cells are D-shaped, 3.5±5 Mm long, and laterally compressed. There is a shallow groove on the left side of the cell. Two ¯agella of similar length emerge subapically and are slightly longer than the cell. The anterior ¯agellum is directed perpendicular to the ventral face of the cell of attached cells. The posterior ¯agellum is reēxed, passing over one face of the cell and then attaching to the substratum by the tip. In swimming cells, the anterior ¯agellum is directed forwards and beats with a sine-wave, and the posterior ¯agellum is directed backwards and trails. Usually moves fast following a spiral path, but sometimes moves slowly. Food particles (bacteria) may be ingested near the posterior part of the ventral groove. Not common.
Remarks. Generally, our observations are consistent with descriptions of Fenchel and Patterson (1988) and Larsen and Patterson (1990). Previous studies reported the size range to be 1.5±10 Mm (Fenchel and Patterson, 1988; Larsen and Patterson, 1990; Vùrs, 1992a, 1992b, 1993a, 1993b; Patterson et al., 1993; Vùrs et al., 1995; Ekebom et al., 1996; Patterson and Simpson, 1996; Tong, 1997 a, 1997b; Tong et al., 1997, 1998; Bernard et al., 1999). This species has been widely found from marine sites in Antarctica, subtropical and tropical Australia, North Atlantic, Baltic, Denmark, England, Gulf of Finland, Greenland and equatorial Paci®c. This species resembles Cafeteria minuta (Ruinen, 1938) Larsen and Patterson, 1990 in general appearance, but is distinguished because C. minuta has a longer anterior ¯agellum. Cafeteria roenbergensis resembles C. marsupialis Larsen and Patterson, 1990 in general appearance and in having a short anterior ¯agellum, but C. marsupialis is larger and has a ventral groove with a posterior channel leading into the cell. It may not be clearly distinguished from Acronema sippewissettensis (Teal et al., 1998), the ¯agella of which are said to be acronematic. Cafeteria roenbergensis may occasionally occupy about 6±20% of the heterotrophic ¯agellate population (Fenchel, 1982; Tong, 1997b) and is cosmopolitan.