Ultrastructure of the enteromonad flagellate Caviomonas mobilis

Caviomonas mobilis was collected from the caecum of mice harbouring a controlled fauna. Phase contrast and immunofluorescence microscopy using an anti-tubulin antibody and electron microscopy demonstrated the presence of one basal body bearing a flagellum and a second barren basal body, both inserted in the face of two cup-like depressions in the nuclear surface, as in other enteromonad/diplomonad genera. Three microtubular fibres arise close to the main basal body: the first, composed of three microtubules cross-linked with a dense structure, lies within a groove above the nuclear surface; the second is oriented antero-dorsally and corresponds to the peristyle as observed by light microscopy; and the third is situated ventrally, below the proximal part of the recurrent flagellum, and corresponds to the funis. There is no mitochondrion, no Golgi body, the endoplasmic reticulum is reduced, there is no cytostome, the cell feeds by pinocytosis and phagocytosis and the division spindle is intranuclear. The cytological characters of Caviomonas are homologous to those of genera which comprise the enteromonad/diplomonad evolutionary lineage, as previously presumed.