Trichostomatida

(invertebrate zoology) An order of ciliated protozoans in the subclass Holotrichia in which no true buccal ciliature is present but there is a vestibulum.

An order of the Holotrichia, composed of a small group of ciliates whose species show some advance in structural complexity over the gymnostomes. No true buccal ciliature is present, but a vestibulum, a passageway leading from the outside of the body into the cytostome or true cell-mouth, is characteristically present. These animals exist in a wide range of habitats. A few forms live in cattle, sheep, and horses, but cause no harm to these hosts. Balantidium is of some medical significance as it contains the sole ciliated protozoan species parasitic in humans. Balantidium coli lives in the large intestine and is the causative agent of the fairly uncommon disease balantidiasis. See also Holotrichia.