Ultrastructure of Trimastix pyriformis (Klebs) Bernard et at.: Similarities of Trimastix species with retortamonad and jakobid flagellates

Trimastix pyriformis (Klebs 1893) Bernard et al, 1999, is a quadriflagellat e, free-living, bacterivorous heterotrophic nanoflagellate from anoxic fres hwaters that lacks mitochondria. Monoprotist cultures of this species conta ined naked trophic cells with anterior flagellar insertion and a conspicuou s ventral groove. Bacteria were ingested at the posterior end of the ventra l groove, but there was no persistent cytopharyngeal complex. The posterior flagellum resided in this groove, and bore two prominent vanes. A Golgi bo dy (dictyosome) was present adjacent to the flagellar insertion. The kineti d consisted of four basal bodies, four microtubular roots, and associated f ibers and bands. Duplicated kinetids, each with four basal bodies and micro tubular root templates, appeared at the poles of the open mitotic spindle. Trimastix pyriformis is distinguishable from other Trimastix species on the basis of external morphology, kinetid architecture and the distribution of endomembranes. Trimastix species are most similar to jakobid flagellates, especially Malawimonas jakobiformis, and to species of the retortamonad gen us Chilomastix. Retortamonads may have evolved from a Trimastix-like ancest or through loss of "canonical" (easily seen with electron microscopy) endom embrane systems and elaboration of cytoskeletal elements associated with th e cytostome/cytopharynx complex.