Description of Mastigamoeba simplex
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Flagellated and non-flagellated forms occur, rounded to elongate, 5 to 21 microns long, fagellated cells are usually ovoid to elongate, with the flagellum up to 40 microns long. The bulk of the nucleus is often located about one third of the cell away from the apex, although an extension of the nucleus connects to the base of the flagellum (this can be difficult to see). Inclusions may be present, although the anterior-most region of the cell is usually hyaline. Some eruptive formation of pseudopodia occurs in the region of the flagellar insertion. Fine, sometimes branching, pseudopodia may also form, especially from the posterior end, sometimes forming a pronounced tail by which the cell attaches to the substrate. When swimming, the flagellum is directed anteriorly. A contractile vacuole in freshwater isolates, usually located posteriorly, and filled by fusion of smaller vesicles.