These monogeneans have both marine and freshwater representatives, and can be identified by their distinctive opisthaptor.
All species have a direct life cycle but a few species are capable of parthenogenetic reproduction.
The prohaptor is usually well developed with various psueudosuckers or cephalic glands present. The main feature is an opisthaptor which may be complex in structure but which is present in only one copy. There may be an anchor composed of several hamuli and supporting bars, marginal hooklets, or a subdivision of the opisthaptor into loculi.