anterior end obliquely truncate, posterior end rounded
length 20–30 µm
periplast with longitudinal ridges, twisted slightly clockwise
one flagellum, almost body length
spherical nucleus below middle
larger paramylon granules often in anterior half
sometimes some tiny paramylon grains at posterior end
Rhabdomonas costata
Rhabdomonas costata I could detect so far only in the Simmelried, where the species occurs rather sporadically. It is easy to distinguish from Menoidium or Astasia, because the cell is not flattened (like Menoidium), has distinct longitudinal ridges and is not metabolic (like Astasia). On Rhabdomonas costata the slender, slightly curved shape is typical, which is transversely truncated at the anterior end.
Fig. 1 a-e:Rhabdomonas costata. L = 29 µm. Different focal planes of a freely swimming specimen. Note the longitudinal ridges (LR) of the pellicle. F = flagellum, Nu = nucleus. Obj. 100 X.
Fig. 2 a-c:Rhabdomonas costata. L = 28 µm. Different focal planes of a second freely swimming specimen. Obj. 100 X.