Petalomonas, S.F.N.Stein, 1859

Lee, Won Je & Patterson, David J., 2000, Heterotrophic flagellates (Protista) from marine sediments of Botany Bay, Australia, Journal of Natural History 34, pp. 483-562 : 520

Petalomonas labrum Lee and Patterson, n. sp.

(fi gures 14c, 15n -p. Type micrograph: fi gure 15p)

Diagnosis. Petalomonas , 11-17 Mm long, with a raised rim around a wide opening of the fl agellar canal.

Description. Cell ovate and elliptical, 11-17 Mm long, 6-10 Mm wide, dorsoventrally fl attened, with a rim surrounding a wide apical opening of the fl agellar canal. Cells have very indistinct or smooth pellicle and the ventral face of the cell is slightly concave. The cell tapers slightly towards the wedge-shaped posterior end. One fl agellum emerges from the long narrow canal and is about as long as the cell or slightly longer. The fl agellum only moves a little when the cell glides forwards. The reservoir is situated equatorially in the right-hand side of the cell. The nucleus is located in the left-hand side of the cell. Rare. Description based on observations of fi ve cells.

Remarks. This species is assigned to Petalomonas because it is rigid, fl attened, has an apical canal opening, one emergent fl agellum and no visible mouth. This species can be clearly distinguished from all other species of the genus Petalomonas by the wide opening of the fl agellar canal and by the raised rim around the opening. It is most similar in size and outline to P. gibbera (see Christen, 1962b), but can be distinguished by the raised margin of the opening, by the smooth pellicle and by the smaller size ( P. gibbera is 20-22 Mm long). Petalomonas ventritracta (see Skuja, 1939) is similar to P. labrum in having a canal with a wide opening, but is distinguished by its shape, its ventral groove and its larger size (24-27 Mm). Some species, such as P. mediocanellata var. pleurosigma Stokes, 1888 , have a wide anterior end, which may indicate a canal with a wide opening.