Polypodium hydriforme

Polypodium hydriforme is a species of parasite attacking the eggs of sturgeon and similar fishes (Acipenseridae and Polyodontidae). It is one of few metazoans living inside the cells of other animals.

Polypodium hydriforme is the only species in the genus Polypodium (monotypic genus). It is also the only species and genus within the whole family Polypodiidae.