They appear to be taken from an entry on the Encyclopedia of Arkansas website, of several stages of the parasite Polypodium hydriforme which develops in the eggs of certain species of fish, including ...

It’s called Polypodium hydriforme, and it’s the closest living relative of all myxozoans. It infects the eggs of sturgeons and paddlefish; as Cartwright says, it’s a caviar parasite.

Their closest relative is Polypodium hydriforme, another cnidarian parasite with a jellyfish-like life stage. How did myxozoas forgo their complex, mascroscopic heritage to become so small and simple?