Odontobius (Nematoda, Monhysteridae) from the baleen plates of whales and its relationship to Gammarinema living on crustaceans

Based on new material, the poorly known nematode species Odontobius ceti Roussel de Vauzème, 1834 is redescribed. It lives on the baleen plates of the baleen whales. It is argued that it belongs to the Monhysteridae sensu Lorenzen. Within this family, Odontobius appears to be most closely related to Gammarinema, species of which live externally on peracarid and decapod crustaceans. It is suggested that Odontobius ceti or its ancestor lived externally on crustaceans which were (or still are?) of nutritional importance to baleen whales and that in the course of feeding on these crustaceans the nematode became adapted to its current biotope.