Cyclidium O.F. Muller, 1773 (ref. ID; 2014) or 1786 (ref. ID; 3690)
Class Oligohymenophora: Subclass Hymenostomata: Order Scuticociliatida (ref. ID; 2014)

[ref. ID; 2014]
Small (about 20 um long) elongated oval ciliate usually somewhat dorso-ventrally compressed. Undulating membrane large and conspicuous forming a prominent pouch or pocket at its posterior end near the oral aperture. Membranellar system stretches down half the body length of sometimes more, unlike that of Uronema which has a small inconspicuous system of membranelles. Membranelles in oral aperture small and shifted towards right. Somatic kinetosomes paired, arranged in about 15 kineties. Truncated apical end free from cilia, truncated terminal pole carries single caudal cilium. Otherwise somatic ciliation is uniformly distributed unlike that of Cristigera. Contractile vacuole posterior. Ovoid macronucleus located anteriorly as in Uronema together within adjacent micronucleus. One species originally described as living in a lorica now thought to be a member of the genus Calyptotricha (Wilbert & Foissner, 1980)
Quote; Colin R. Curds, Michael A. Gates and David McL. Roberts "British and other freshwater ciliated protozoa Part II Ciliophora: Oligohymenophora and Polyhymenophora" Cambridge University Press, 1983 (ref. ID; 2014)

Cyclidium citrullus Cohn, 1865 (ref. ID; 1622, 2245, 3116) or 1866 (ref. ID; 3593, 4611) reported year? (ref. ID; 1219, 3342, 5462) reported author and year? (ref. ID; 191, 3759)
Description; Ventral surface flattened; anterior pole without cilia, 1 long caudal cilium inserted in a hollow at the posterior end, 15-16 ciliary meridians; conspicuous external undulating membrane of approximately two-third length of body, forming a pocket around the cytostomal groove; membrane with 2 situations; when inactive the membrane is concealed in a groove situated at the posterior part of the cell; 1 spherical macronucleus and a single micronucleus are located anterior; contractile vacuole at the posterior end of the cell; a very characteristic feature is that the organism remains motionless when feeding, its cilia spread wide and the undulating membrane in action. (ref. ID; 1219)
This species is thermophilic ciliate. It can reproduce at a wide temperature range (18 ~ 47 degrees C). (ref. ID; 3759)
Measurements; Length 15-40 um, mean about 30 um. (ref. ID; 1219)
9-23 x 9-13 um. (ref. ID; 3342)
Cyclidium glaucoma (O.F. Muller, 1773) (ref. ID; 2128, 4488, 4611) or 1786 (ref. ID; 1308, 1335, 1622, 1629, 3116, 3593) reported year? (ref. ID; 1219, 2245, 2249, 3698, 4674, 5624) reported author and year? (ref. ID; 191)
Description; Body ovoid with cilia-free anterior end; 1 long caudal cilium; 10 (rarely 11) ciliary meridians; the large undulating membrane is free of sinuations and approximately one-half the length of body a full description of the buccal organelles is given by Berger & Thompson (1960); in addition to the undulating membrane, there are 3 definitive membranelles that are difficult to observe in the living condition; unlike C. citrullus, this species lacks a post-oral longitudinal groove; 1 spherical macronucleus and a single micronucleus are located near the anterior end of the body; the contractile vacuole is posteriorly situated. (ref. ID; 1219)
Ellipsoid with narrowed, rather distinctly set off anterior end (frontal plate), laterally slightly flattened. Macronucleus invariably in anterior third of cell, distinguished to 2-4 small globules in about half of specimens. Micronucleus in anterior indentation of macronucleus, compact and thus conspicuous in live cells, rarely and only faintly impregnates with protargol. Contractile vacuole invariably in posterior end of cell, with single excretory pore (diameter about 1 um) at end of kinety 2, rarely between kineties 2 and 3. Somatic cilia in vivo about 8 um long, basal bodies paired in anterior third of cell, however, not all dekinetids have both basal bodies ciliated. Caudal cilium conspicuous, about 20 um long. Cilia not condensed in posterior hall of first kinety left of oral apparatus. Basal bodies not paired in anterior half of paroral membrane. (ref. ID; 2128)
Measurements; Length 15-30 um, mean about 20 um. (ref. ID; 1219)
Size in vivo about 17-22 x 8-11 um, usually 19 x 9 um. (ref. ID; 2128)
35 um long. (ref. ID; 2249)
Cyclidium lanuginosum Penard, 1922 (ref. ID; 1219, 1622, 2245)
See; Calyptotricha lanuginosum (ref. ID; 4611)
Description; Body elongate-ovoid, dorsally flattened in contrast to the other species of the genus, which are ventral flattened; 2 long frontal cilia are inserted close to the anterior pole; 1 long caudal cilium; about 22 longitudinal rows of rather short cilia; undulating membranelle approximately three-quarter of the body length; macronucleus in the anterior region; contractile vacuole dorsally positioned and close to the posterior end; according to Wilbert (1969) this species lives within a thin tube-shaped shell or case that is secreted by the organism itself and is attached to the substrate (Plant material or artificial surface such as glass slides); the ciliate is attached to the wall of its case by the flattened dorsal part of the body. The shell is abandoned immediately in the event of any disturbance; perhaps this is the reason why this particular feature of C. lanuginosum escaped earlier observation. (ref. ID; 1219)
Measurements; Length 35-40 um. (ref. ID; 1219)
Cyclidium litomesum Stokes, 1884 (ref. ID; 1622) reported year? (ref. ID; 1618)
Description; Dorsal surface slightly convex with a depression in middle; ventral surface more or less concave; cilia long; in fresh water. (ref. ID; 1618)
Measurements; About 40 um long. (ref. ID; 1618)
Cyclidium muscicola Kahl, 1931 (ref. ID; 3593, 4861) reported year? (ref. ID; 4842) reported author and year? (ref. ID; 1622)
Improved diagnosis; Size in vivo 14-20 x 9-13 um. Usually 1 macronucleus and 1 micronucleus. Contractile vacuole distinctly subterminal, viz. right of peristomial vertex with excretory pore between kineties 1 and 2.9-10 somatic kineties, anterior end of kinety 1 polymerized. Adoral membranelle 2 small, laterally attached to membranelle 1. (ref. ID; 4861)
Redescription; The populations investigated were found in meadow soils near the town of Salzburg and in Hawaii. They are very similar, at least in vivo, to those observed in Costa Rica and in other soils world-wide. Size in vivo 14-20 x 9-13 um. Shape slenderly to broadly ellipsoid, frontal plate distinct, laterally sometimes inconspicuously flattened. Nuclear apparatus in anterior body half, usually 1 globular macronucleus disintegrated into as many as 6 smaller spheres in about 20% of specimens. Micronucleus globular, attached to macronucleus in Salzburg population, often distant from macronucleus and in anterior end of cell in Hawaii population, difficult to recognize in living cells. Contractile vacuole on average exactly right of peristomial vertex, i.e. distinctly subterminal, with single excretory pore located between kineties 1 and 2, connected to kinety 2 with faint silverline. Extrusomes about 3 um, long, cuneate with thicker end anchored in cortex, often difficult to recognize in living cells, probably absent in some cells or populations. Cortex distinctly furrowed. Cytoplasm colourless, contains some small fat droplets and usually many 2-5 um sized food vacuoles with bacterial residues. Movement as in C. glaucoma, i.e. jumping and resting; when resting and feeding cilia of anterior third directed anteriorly, those behind posteriorly. Rarely, population have been observed which, although resting, did not distinctly jump. Somatic infraciliature and silverline system similar to other members of genus. Cilia 8-10 um long, rather stiff, 4-7 cilia very closely spaced in anterior portion of first kinety right of paroral membrane. Somatic kineties regularly spaced, of four populations analyzed two had mostly 9 and two mostly 10 kineties; each kinety commences with 1-4 dikinetids, depending on population. Caudal cilium at least as long as cell, inclined to ventral side, proximal portion very fine and curved. Oral apparatus extends from anterior end to second third of cell. Adoral membranelles inconspicuous, membranelle 2 distinctly smaller than in C. glaucoma, i.e. composed of about 12 basal bodies only and indistinctly separate from membranelle 1. Cilia of undulating membrane 8-10 um long, form conspicuous velum during feeding, directed backwards in swimming and resting cell. (ref. ID; 4861)
Idetification; The populations studied perfectly match the short by appropriate original description. Cyclidium muscicola is easily recognized by its small size and the unusual location of the contractile vacuole, also emphasized by Kahl (1931). Superficially observed, it could be confused with the similarity sized C. glaucoma, which, however, occurs very rarely in terrestrial biotopes (Foissner 1987) and differs from C. muscicola not only the terminal location of the contractile vacuole but also by the higher number (10-11) of somatic kineties and the larger adoral membranelle 2 (Berger & Thompson 1960, Didier & Wilbert 1981, Foissner et al. 1994). However, another Cyclidium species occurs in many soils, possibly C. terricola Kahl, 1931, which resembles C. muscicola, especially in the subterminal location of the contractile vacuole. This species is larger (30-35 um), distinctly flattened and has 12 somatic kineties (Foissner, unpubl.); it is apparently rather similar to C. bonneti Groliere, 1980. Cyclidium muscicola has also been redescribed by Song Weibo & Wilbert (1989). This population differs distinctly from my specimens by its larger membranelle 2, which is not attached to membranelle 1, and the contractile vacuole pore which is located more distally and not beside but at end of kinety 2. Furthermore, it is larger (20-30 x 12-17 um) and the cilia are very widely spaced in the anterior end of somatic kinety 1. Song Weibo & Wilbert (1989) found this population in an eutrophic pond in Germany, while Kahl (1931) discovered C. muscicola in terrestrial mosses. I thus suggest considered my soil population as the species described by Kahl (1931). The population studied by Song Weibo & Wilbert (1989) is possibly a new species or an ecoform of C. bonneti Groliere, 1980. (ref. ID; 4861)
Type specimens deposited; Slides with type and voucher specimens have been deposited in the Oberosterreichische Landesmuseum in Linz (LI), Austria. Relevant specimens are marked by a black ink circle on the cover glass. (ref. ID; 4861)
Cyclidium pellucidum Kahl (ref. ID; 3342) reported author and year? (ref. ID; 1622)
Measurements; 43-47 x 22 um. (ref. ID; 3342)