Description of Acanthamoeba: Locomotive form usually between 12 and 40 microns 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 two layers; a thick, wrinkled outer ectocyst and an inner polygonal endocyst and a wall pore with operculum. 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. So-called marine strains tend not to grow on full salinity media for more than a few generations. Some Acanthamoeba have been implicated in infections of the human cornea. Type species: A. castellanii (Douglas, 1930). Most species distinguished by cyst morphology.