Hysterocinetidae

Thigmotrich ciliates, prominent, anterior, thigmotactic sucker; may have segments of anterior kineties in unciliated area; oral infraciliature reduced and at posterior with oral polykinetid 2, two kinetosomes wide, in two segments with a peristomal segment around the posterior pole and an infundibular segment; symbionts in oligochaetes and molluscs; hysterocinetids and paraptychostomids share some features with astomes, being used to justify the placement of the Scuticociliatia and Astomatia in the same taxon: an anterior sucker-like organelle occurs in these two families and also in haptophryid astomes; and division by chain-formation occurs in hysterocinetids (e.g., Kozloffia, and some astomes (e.g., Family Haptophryidae; Family Radiophryidae).

Hysterocinetid scuticociliates, division by catenulation (chain formation); symbionts of oligochaetes (e.g., Alma).

Hysterocinetid scuticociliates, sucker with 6-7 somatic kineties extending into thigmotactic field; symbionts of oligochaetes.