These are parasites of poikilothermic vertebrates.
Adults live in the intestine of fish, amphibians and reptiles. Crustaceans are the intermediate host. Paratenic hosts may be used.
Main longitudinal lacunar canals are dorsal and ventral. Giant nuclei are present in the body wall and lemnisci. Cement glands in the male are syncytial. There are two ligament sacs in the female and they persist throughout life.