Myxosporidea (phylum Protozoa, subphylum Cnidospora) A class of protozoa, which parasitize invertebrates and lower vertebrates, particularly fish, often with fatal consequences for the host. The spores contain a coiled polar filament. When a spore is ingested by a new host the filament is extruded and attaches the spore to the gut wall of the host. There are three orders.

Cnidospora (phylum Protozoa) A sub-phylum of protozoa which form complex spores containing threads (polar filaments) which can be extruded, and function in attachment. There are two classes. They are parasites in a range of vertebrate and invertebrate hosts.