''Filicollis anatis'' is an

endoparasite Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has c ...

in the Polymorphidae family of

thorny-headed worm Acanthocephala (Greek , ', thorn + , ', head) is a phylum of parasitic worms known as acanthocephalans, thorny-headed worms, or spiny-headed worms, characterized by the presence of an eversible proboscis, armed with spines, which it uses to p ...

s. Adults have been found to occur in waterbirds such as ducks, where they cause a condition known as filicollosis. Larval stages occur in invertebrate hosts such as crayfish. A study in the

Chernihiv Chernihiv ( uk, Черні́гів, , russian: Черни́гов, ; pl, Czernihów, ; la, Czernihovia), is a city and municipality in northern Ukraine, which serves as the administrative center of Chernihiv Oblast and Chernihiv Raion within ...

region of

Ukraine Ukraine ( uk, Україна, Ukraïna, ) is a country in Eastern Europe. It is the second-largest European country after Russia, which it borders to the east and northeast. Ukraine covers approximately . Prior to the ongoing Russian invas ...

found that ''F. anatis'' infected ducks throughout their grazing period, but not in the winter; it also found that the parasite's eggs could remain viable throughout the winter when buried in mud under natural conditions. Acanthocephalans such as ''F. anatis'' form capsules in their intermediate arthropod hosts to protect the developing larvae from the host immune system. ''F. anatis'' forms its capsules primarily by secreting material during the initial (acanthellar) stage after infecting the intermediate host.

References

Polymorphidae Animals described in 1788 Endoparasites {{acanthocephalan-stub