Circumscription: Biflagellated gliding protist, heterotrophic, one flagellum projecting anteriorly, one trailing, with a posterio-lateral ingestion apparatus. Argued by some to be related to bicosoecids. Ultrastructural identity: Tubulocristate mitochondria, two flagella giving rise to four microtubule roots; no hairs, scales, or other excrescences attached to flagella or cells surface. One of two studies shows osmiophilic structures in support of a mouth linked to roots arising from the basal bodies. Synapomorphy: As yet unspecified but probably will relate to the structure of the feeding apparatus. Composition: One species, Caecitellus parvulus.