Family Cycloposthiidae

This spirotrichasin, entodiniorid family differs from the related Ophryoscolecidae in that its members have 2 or more bands of membranelles in addition to the adoral zone, instead of 1. Most members of this family occur in equids, but others occur in tapirs, rhinoceroses and elephants, which are related to them. One genus occurs in anthropoid apes.

Genus Cycloposthium

The body is large and elongate barrelshaped. The cytostome is in the center of a retractile, conical elevation at the anterior end. The adoral zone of membranelles is conspicuous. There are open ring zones of membranelles near the posterior end on the dorsal and ventral sides. The pellicle is ridged. There is a club-shaped skeletal plate. A row of several contractile vacuoles runs along the band-formed macronucleus.

Cycloposthium bipalmatum (Fiorentini, 1890) Bundle, 1895 is more or less rectangular, slightly compressed laterally, with a truncate anterior end and a tapering posterior end with a tail-like structure. It measures 80 to 127 by 35 to 57 u. A longitudinal groove and a light, linear skeletal plate are present on the left side. The macronucleus is hooked anteriorly, and the micronucleus is located near its middle. There are 4 contractile vacuoles. Hsiung (1930) found this species in the cecum of 38 and the colon of 8 out of 46 horses in Iowa.

C. dentiferum Gassovsky, 1919 measures 140 to 220 by 80 to 110 u. It resembles C. bipalmatum but has a ventral dentiform projection, and the anterior end of its macronucleus is not hooked. The cuticle is not corrugated. A longitudinal groove is present on the left side, but the linear skeletal plate is quite indistinct. There are 4 to 6 contractile vacuoles. Hsiung (1930) found this species in the cecum of 16 and the colon of 2 out of 46 horses in Iowa.

C. ishikawai Gassovsky, 1919 differs from all other species of the genus in that the posterior arches of membranelles are nonretractile. It measures 230 to 280 by 110 to 130 u. Hsiung (1930) did not find it in Iowa horses.

C. edentatum Strelkov, 1928 resembles C. bipalmatum but has 6 to 7 contractile vacuoles. It measures 146 to 230 by 68 to 93 u. Hsiung (1930) found this species in the cecum of 11 and the colon of 2 out of 46 horses in Iowa.

C. piscicauda Strelkov, 1928 resembles C. bipalmatum but lacks both the longitudinal groove and skeletal plate on the left side. It measures 125 to 190 by 44 to 80 u. It has 4 or 5 contractile vacuoles. Its posterior end forms a tail resembling that of a fish. Hsiung (1930) did not find this species in Iowa horses.

C. scutigerum Strelkov, 1928 differs from C. bipalmatum in having a shieldlike skeletal plate interrupted by 2 longitudinal grooves on the left side instead of a simple, narrow plate. It measures 132 to 210 by 63 to 90 u and has 5 or 6 contractile vacuoles. Hsiung (1930) found this species in the cecum of 24 and the colon of 4 out of 46 horses in Iowa.

C. affinae Strelkov, 1928 differs from C. bipalmatum in having a heavy skeletal plate and in that the micronucleus is near the anterior end of the macronucleus. It measures 92 to 141 by 45 to 58 u. Hsiung (1930) found this species in the cecum of 3 and the colon of 1 out of 46 horses in Iowa.

C. corrugatum Hsiung, 1930 measures 135 to 195 by 70 to 112 u. It has a ventral dentiform projection, and its cuticle is corrugated. The anterior end of its macronucleus is not hooked. The linear skeletal plate is quite indistinct. There are 4 or 5 contractile vacuoles. Hsiung (1930) found this species in the cecum of 7 and the colon of 1 out of 46 horses in Iowa.

Genus Spirodinium

The body is elongate and more or less fusiform, with an adoral zone of membranelles at the anterior end. An anterior ciliary zone encircles the body at least once, and a posterior ciliary arch spirals half-way around the body. There is a dorsal cavity of unknown function lined with stiff rods.

Spirodinium equi Fiorentini, 1890 measures 77 to 180 by 30 to 74 u. Its macronucleus is elongated, with rounded ends. There is a large contractile vacuole just back of the anterior membranelles. Hsiung (1930) found this species in the colon of 3 out of 46 horses in Iowa.

Genus Triadinium

The body is more or less helmetshaped and compressed, with an adoral zone of membranelles at the anterior end. There are ventral and dorsal posterior zones of membranelles. There may or may not be a caudal projection.

Triadinium caudatum Fiorentini, 1890 measures 50 to 105 by 36 to 85 u and has a long, slender tail. The macronucleus is bent like a question-mark. There is a single contractile vacuole. Hsiung (1930) found this species in the colon of 3 out of 46 horses in Iowa.

T. galea Gassovsky, 1919 measures 58 to 88 by 50 to 70 u and lacks a tail. It has a long macronucleus running longitudinally along the left surface, and 2 contractile vacuoles. Hsiung (1930) found this species in the colon of 3 out of 46 horses in Iowa.

T. minimum Gassovsky, 1919 measures 32 to 50 by 31 to 42 u and has a slender tail. The macronucleus is ellipsoidal. There is a single contractile vacuole. Hsiung (1930) found this species in the colon of 2 out of 46 horses in Iowa.

Genus Tetratoxum

The body is slightly compressed and has 2 anterior and 2 posterior zones of membranelles.

Tetratoxum unifasciculatum (Fiorentini, 1890) Gassovsky, 1919 measures 104 to 168 by 62 to 100 u. It is irregularly elliptical, with both ends rounded, and has 7 to 9 longitudinal, cuticular ridges on both the dorsal and ventral surfaces of the body. Lateral cuticular extensions at the posterior end form 2 caudal sheaths. The macronucleus is elongate, with a short hook at the anterior end. There is a large contractile vacuole under its curvature. Hsiung (1930) found this species in the colon of 2 out of 46 horses in Iowa.

T. excavatum Hsiung, 1930 measures 95 to 135 by 55 to 90 u. It differs from T. unifasciculatum in having a deep elliptical excavation covered by a flap of cuticle at its anterior end, and its cuticular ridges are more prominent and the adjacent ones further apart. Hsiung (1930) found this species in the colon of 1 out of 46 horses in Iowa.

T. parvum Hsiung, 1930 measures 67 to 98 by 39 to 52 u. It differs from the other 2 species in lacking longitudinal cuticular ridges. Hsiung (1930) found this species in the colon of 1 out of 46 horses in Iowa.

Genus Tripalmaria

There is an adoral zone of membranelles at the anterior end and also 2 dorsal and 1 ventroposterior tuft-formed zones of membranelles. The macronucleus is shaped like an inverted U. A synonym of this genus is Tricaudalia Buisson, 1923.

Tripalmaria dogieli Gassovsky, 1919 measures 77 to 123 by 47 to 62 u. Beneath the right side it has skeletal plates forming a horseshoe with its open end directed posteriad. Hsiung (1930) found this species in the colon of 3 out of 46 horses in Iowa.

Genus Cochliatoxum

There is an adoral zone of membranelles at the anterior end and also 1 anterodorsal, 1 posterodorsal and 1 posteroventral zone of membranelles. The anterior end of the macronucleus is curved.

Cochliatoxum periachtum Gassovsky, 1919 is more or less cylindrical, with both ends rounded, and measures 210 to 370 by 130 to 210 u. There is a contractile vacuole. Hsiung (1930) found this species in the colon of 1 out of 46 horses in Iowa.

Genus Ditoxum

There is a large adoral zone of membranelles near the anterior end and also anterodorsal and posterodorsal zones of membranelles. The macronucleus is curved and club-shaped.

Ditoxum funinucleum Gassovsky, 1919 is elliptical with both ends rounded, slightly flattened bilaterally, and measures 135 to 203 by 70 to 101 u. It has a single contractile vacuole. Hsiung (1930) found this species in the colon of 2 out of 46 horses in Iowa.