Tetrahymena (tet-ra-high-men-a) is an oligohymenophoran ciliate. Widely used in laboratory studies, and axenic (bacteria-free) cultures are maintained within high protein medium. In nature often associated with damaged animals or dead tissue. This occurrence within the cytoskeleton where they may feed on residual tissue (pieces left behind if the cytoskeleton has been shed) or on the body tissue (if the crustacea was damaged) is a good example of where this genus might be found in nature. Dark ground.