Polymorphidae
The thorny-headed worm family Polymorphidae contains endoparasites which as adults feed mainly in fish and aquatic birds. When this taxon was erected by Meyer in 1931, a subfamily Polymorphinae was established in it. As the Polymorphidae as presently understood would then be monotypic, with no basal genera outside the Polymorphinae, the proposed subfamily is redundant for the time being and therefore most modern treatments simply omit it. "Polymorphus minutus" is an economically significant parasite in goose and duck farming. Species. Polymorphidae contains the following species: Andracantha Andracantha gravida Ardeirhynchus "Arhythmorhynchus" "Bolbosoma" "Corynosoma" "Diplospinifer" "Filicollis" "Ibirhynchus" "Neoandracantha" Polymorphus The  genus polymorphus uses amphipod crustaceans as intermediate hosts and various birds as final hosts. The genus used to be a larger group, but species that were formerly placed in the genus have now been placed in the genus "Profilicollis" based on morphological characteristics and the use of decapod crustaceans as intermediate hosts. "Profilicollis" "Pseudocorynosoma" Southwellina Tenuisoma "T. tarapungi" was found in the intestines of the red-billed gull ("Chroicocephalus scopulinus") on the coast of Otago, New Zealand.