These tapeworms are unusual in having only a single set of reproductive organs and a scolex possessing only shallow loculi. Nevertheless, their lack of a gut gives away their cestode identity. These are intestinal parasites of freshwater fishes. Despite their poorly developed scolex, they can cause considerable pathology localized around their scolex. They stimulate the host to proliferate a nodule around their scoleces, and often numerous worms will be observed attached within the same nodule.