Family CYCLIDIIDAE Ehrenberg, 1838

Body ovoid to elongate-ovoid, generally small to very small, with sparse ciliation and distinctive caudal cilium; cytostome variable in position and buccal ciliature less prominent than in the Pleuronematidae; macronucleus and large micronucleus often located in anterior third of body; widely distributed forms, from fresh-water, brackish, marine, interstitial, edaphic, and even coprozoic habitats.

[Note: Fig. 39, p48, is probably not a Cyclidium.]

Abathostoma Berger [unpublished]. Single species.
Calyptotricha Phillips, 1882. Single species.
Cyclidium O. F. Müller, 1786. Many species.
Mesogymnus Berger [unpublished] . Single species.
Incertae sedis:
Cristigera Roux, 1899, many species,
Ctedoctema Stokes, 1884, few species,