Ancyromonas cells are small, less than 10 µm. They glide and have two flagella. The posterior flagellum inserts below the apex of the cell and trails to the rear; the anterior flagellum may be thin or of normal size, and it may sometimes be absent. There is usually a groove from the point of insertion of the posterior flagellum and along the lateral margin of the cell. The cells wobble as they glide.
This genus is widespread and common. It has been reported from marine and terrestrial habitats. The organisms probably consume bacteria. Three species are currently recognised, of which only two (A. sigmoides and A. melba) have been reported recently (Patterson and Simpson, 1986).
On the basis of comparisons of small subunit ribosomal RNA genes, Atkins and co-workers (Atkins et al., 2000) have suggested that Ancyromonas is closely related to the lineage which gave rise to animals and fungi, although sister group relationships have yet to be resolved.
The type species is A. sigmoides Kent 1880.
The genus has been the subject of one ultrastructural study (Mylnikov 1990) under the generic name Heteromita. The genus has mitochondria with flat cristae. The cell surface is supported by materials within and external to the cell membrane. There are 'ball and cone' style extrusomes present. The most similar taxa are Metopion and Caecitellus, but Ancyromonas can be distinguished from both by the site at which the anterior flagellum inserts.
Description of Ancyromonas