Temnocephalid flat worm, Scanning electron micrograph (SEM). Temnocephalidae platyhelminthes species are ectocommensal ( living in a commensal relationship on the exterior of another organism) on freshwater crustaceans, in particular crayfish, so they occur wherever the hosts occur. They live attached to the outside body surface of the host or within the branchial chamber. The host crustacean is not harmed by the temnocephalid flat worm. Two to six finger-like tentacles are found anteriorly with a single posterior sucker. Magnification: x20 when printed at 10 centimetres high.