Ichthyophonus hoferi is a single-celled protist that occupies a key phylogenetic position to understand the origin of animals. It has chitin cell wall, hyphae, and an amoeboid stage. It is a common parasite of marine and freshwater fishes.
In fish, I. hoferi causes hemorrhages and fin and skin rot, destroys muscle, and induces ova to develop without spermatic fertilization through a toxin.