Genus Acanthamoeba Volkonsky, 1931
Diagnosis: Locomotive form usually between 12 and 40 µm in length. Pseudopodia clear, slowly eruptive, and occasionally branching at base. With numerous, slender, and tapering subpseudopodia (acanthopodia) giving the cell a spiny appearance. Cytoplasm without crystals but frequently with small lipid globules and an obvious contractile vacuole. Nucleus spherical with a central nucleolus. Posterior uroid temporary. Cysts common, often with 2 layers, a thick, wrinkled outer ectocyst and an inner polygonal endocyst and a wall pore with operculum.
Type species: Acanthamoeba castellanii (Douglas, 1930).
Ecology: Possibly the most commonly isolated genus of all naked amoebae from freshwater and soil habitats. Acanthamoebae have also been isolated from salt water of low salinity, presumably from cysts.
Remarks: Some Acanthamoeba have been implicated in infections of the human cornea (Acanthamoeba Keratitis) and include: A.castellani, A. polyphaga, A. hatchetii, A. culbertsoni, A.rhysodes and A. griffin.
At least 35 named species which can be distinguished, with difficulty, on the basis of their cyst morphology, immunofluorescence and on isoenzyme structure. Non-morphological procedures (i.e. chemotaxonomic approaches) have been applied to the genus and readers should consult Byers et al. (1983), Costas and Griffiths (1985), McLaughlin et al. (1988), Johnson et al. (1990).