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Description of SaccamoebaLocomotive form active but not eruptive. Genus contains the largest of the hartmannellids, up to 175 µm in length, and shares features with members of the Amoebidae. For example, many species have cytoplasmic crystals and a villous or papillate knob uroid. However, floating form has irregularly rounded pseudopodia rather than the radiating pseudopodia found in most Amoebidae. Mitochondria often elongate. Frequently with bulging posterior contractile vacuole(s). Nucleus with prominent central nucleolus. Cysts reported in some species. Where studied, cell surface at ultrastructural level with cup-like structures. Seven species described from both freshwater and marine habitats. Type species: S. lucens Frenzel, 1892.