Urceolus cyclostomus
(Stein) Mereschkowsky, 1879
Most likely ID: n.a.
Synonym: n.a.
Sampling location: Simmelried, Ulmisried
Phylogenetic tree: Urceolus cyclostomus
Diagnosis:
- body flask-shaped or oviform
- posterior end tapered or round
- length 25–40 µm
- neck funnel-like
- cytostome with rod-shaped ingestion organelle
- reservoir with associated contractile vacuole
- distinct striation of pellicle
- spherical nucleus large, in posterior half
- a single flagellum, 2–3 of body length
I only very rarely find Urceolus cyclostomus. Mostly the specimens are mixed with detritus flakes. The species is easy to recognize by the funnel-like mouth opening and the distinct spiral striation of the pellicle, which runs counterclockwise. The rod-shaped ingestion organelle is difficult to recognize in unsquashed specimens (s. fig. 1 d). The comparatively large nucleus is located in the rear third of the body (s. fig. 1 d). The flagellum is very long. When swimming, only the distal end rotates. Skuja (1956) also describes specimens with a broadly rounded posterior end (s. drawing above); in my population all specimens had a pointed posterior end.
Fig. 1 a-d: Urceolus cyclostomus. L = 37 µm. Different focal planes of a freely swimming specimen. CV = contractile vacuole, F = flagellum, IO = rod-shaped ingestion organell, Nu = nucleus, RE = reservoir. Obj. 100 X.