The Litostomatea are a class of ciliate protists. Until recently, the class Litostomatea was divided into two groups, the Haptoria and the Trichostomatia. However, new genetic information has resulted in the resurrection of a third subclass, Rhynchostomatia, first proposed by A. W. Jankowski in 1980. The Haptoria includes mostly carnivorous forms, for instance Didinium, a species of which preys primarily on the ciliate Paramecium. The Trichostomatia (trichostomes) are mostly endosymbionts in the digestive tracts of vertebrates. These include the species Balantidium coli, which is the only ciliate parasitic in humans. The Rhynchostomatia include two free-living genera previously included among the Haptoria, but now discovered to be genetically distinct from them, the Dileptida and the Trach