Family Paraisotrichidae

In this holotrichasin, trichostomorid family, somatic ciliation is complete, and there is an anterior tuft of longer cilia. The mouth is subterminal, opening just posterior to the concretion vacuole.

Genus Paraisotricha

The cilia form more or less spiral longitudinal rows. The contractile vacuole is posterior.

Paraisotricha colpoidea Fiorentini, 1890 is ovoid, measures 70 to 100 by 42 to 60 u and has 34 to 40 rows of cilia. The macronucleus is a thick, ellipsoidal disc. There is a large concretion vacuole at the anterior end. Hsiung (1930) found this species in the cecum of 21 and the colon of 6 out of 46 horses in Iowa.

P. beckeri Hsiung, 1930 resembles P. colpoidea but has only 11 rows of cilia. It measures 52 to 98 by 30 to 52 u. Hsiung (1930) found it in the cecum of 8 and the colon of 1 out of 46 horses in Iowa.

P. minuta Hsiung, 1930 resembles P. colpoidea but has only 20 rows of cilia and measures 38 to 68 by 27 to 36 u. Hsiung (1930) found it in the cecum of 31 and the colon of 3 out of 46 horses in Iowa.