macronucleus globular with an adjacent micronucleus
posterior sixth of body naked
one caudal cilium
movement jumping and spinning
Urotricha ovata
Urotricha ovata is a widespread ciliate, which I could detect in almost all my localities. Especially in old samples with decaying plant masses it is often found.
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It is easy to confuse Urotricha ovata with the similar species Urotricha armata. The latter, however, has a dense fringe of extrusomes arranged in parallel to each other. In Urotricha ovata, the extrusomes are scattered under the pellicle and are not arranged in parallel (s. figs. 2 a and 2 b). In addition, the number of longitudinal rows of cilia in Urotricha armata is much higher (35–51) than in Urotricha ovata, where there are only 19–27 rows (s. fig. 1 b).
Fig. 1 a-b:Urotricha ovata. L = 43 µm. Two focal planes of a freely swimming specimen. Note the longitudinal rows of cilia (CR). This specimen has 24 rows of cilia. CC = caudal cilium, CV = contractile vacuole, CP = cytopharynx, Ma = macronucleus, Mi = micronucleus. Obj. 60 X.
Fig. 2 a-d:Urotricha ovata. L = 43 µm. Four focal planes of a slightly squashed specimen. Note that the posterior sixth of the body is a cilia-free zone (CZ). CC = caudal cilium, CV = contractile vacuole, CP = cytopharynx, EX = extrusomes, Ma = macronucleus, OF = oral flaps. Obj. 100 X.
Fig. 3 a-b:Urotricha ovata. L = 42 µm. Two focal planes of a slightly squashed specimen. CC = caudal cilium, Ma = macronucleus, OB = oral basket. Obj. 100 X.