(Penard, 1922) Foissner, Berger & Kohmann, 1994
Most likely ID: n.a.
Synonym: Urotricha gracilis, Holophrya gracilis
Sampling location: Simmelried
Phylogenetic tree: Apsiktrata gracilis
- cell ovoid, tapering slowly posteriorly, cross section round
- length 50–70 µm, widht 25–35 µm
- basket of trichites straight to slightly obliquely inserted
- anterior end of basket with refractive collar
- spherical nucleus with central nucleolus or some peripheral nucleoli in anterior half
- one micronucleus adjacent to macronucleus
- contractile vacuole in posterior third
- about 30 µm long caudal cilium
- extrusomes rod-shaped, 4 µm long
Apsiktrata gracilis is the most common prostomatid ciliate in the mud of Simmelried. It is in almost all samples present, sometimes in masses. The species can be easily identified by the thickened ends of the trichites of the basket, which together form an apikal, refractive collar (s. fig. 3). The basket of trichtites is often obliquely inserted, which can be easily seen in free swimming and spinning specimens. In addition, this ciliate has a rather long caudalcilia. In my population, all of the specimens I examined were filled with clearly visible symbiotic bacteria. Interestingly, these are not mentioned by any of the earlier authors, including Foissner, who published an accurate redescription in 1984 (still under Holophrya gracilis). Originally this species was described as Urotricha gracilis by Penard. Later Kahl placed it to Holophrya. Finally Foissner, Berger and Kohmann transferred this species from the genus Holophrya to the newly created genus Apsiktrata, because in contrast to Holophrya and Prorodon species of the genus Apsiktrata do not possess a dorsal brush.
Fig. 1 a-d: Apsiktrata gracilis. L = 65 µm. A freely swimming specimen (a) is fixed and squashed during reduction of the layer thickness (b – c). CC = caudal cilium, CV = contractile vacuole, Ma = macronucleus, OA = oral aperture. Obj. 100 X.
Fig. 2 a-d: Apsiktrata gracilis. L = 52 µm. Different focal planes of a second, freely swimming specimen. Note the basket of trichtites (TB) inserted obliquely. CC = caudal cilium, CV = contractile vacuole, Ma = macronucleus, Mi = micronucleus. Obj. 100 X.
Fig. 3: Apsiktrata gracilis. L = 54 µm. This slightly squashed specimen has fed on small algae and cyanobacteria. Note the thickened anterior ends of the trichites appearing as a refractive collar (RC). Obj. 100 X.
Fig. 4 a-b: Apsiktrata gracilis. L = 60 µm. Two focal planes of a slightly squashed specimen. Obj. 100 X.
Fig. 5: Apsiktrata gracilis. The strongly squashed specimen shown in figs. 4 a-b. Beneath the pellicle the delicate extrusomes (EX) are visible. The cytoplasm is completely filled with symbiotic bacteria (SB) of different shape and size. TB = trichites of the basket. Obj. 100 X.