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 Schmidt, 1975 contains many species:

Ardeirhynchus

Ardeirhynchus Dimitrova and Georgiev, 1994

Arhythmorhynchus

Arhythmorhynchus Lühe, 1911

Bolbosoma

There are twelve species assigned to the genus Bolbosoma Porta, 1908

Corynosoma

Corynosoma Lühe, 1904 contains many species Diplospinifer Fukui, 1929

Filicollis

Filicollis Lühe, 1911 contains two species.

Ibirhynchus

Ibirhynchus García-Valera, Pérez-Ponce de León, Aznar and Nadler, 2011

Neoandracantha

Neoandracantha Amin & Heckmann, 2017 is a monotypic genus containing only Neoandracantha peruensis Amin & Heckmann, 2017

Polymorphus

The genus polymorphus Lühe, 1911 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

Profilicollis Meyer, 1931 contains many species:

Pseudocorynosoma

Pseudocorynosoma Aznar, Pérez-Ponce de León & Raga, 2006 contains several species:

Southwellina

Southwellina Witenberg, 1932 contains three species:

Tenuisoma

Tenuisoma contains one species: T. tarapungi was found in the intestines of the red-billed gull (Chroicocephalus scopulinus) on the coast of Otago, New Zealand.