Circumscription: Cell with two flagella arising at the head of a ventral groove, heterotrophs, and freeliving. Mostly from anoxic or organically enriched sites. Ultrastructural identity: Amitochondriate, with two flagella and with three associated basal bodies, giving rise to three major microtubular roots, two of which support the margins of the ventral groove with associated non-microtubular material. Recurrent flagellum with three vanes. No extrusomes, no discrete ingestion apparatus but with dictyosomes. Synapomorphy: Excavate flagellates with three basal bodies. Type species: Carpediemonas membranifera.