Unionida

Unionida is a monophyletic order of freshwater mussels, aquatic bivalve molluscs. The order includes most of the larger freshwater mussels, including the freshwater pearl mussels. The most common families are the Unionidae and the Margaritiferidae. All have in common a larval stage that is temporarily parasitic on fish, nacreous shells, high in organic matter, that may crack upon drying out, and siphons too short to permit the animal to live deeply buried in sediment.

Iridinidae is a family of medium-sized freshwater mussels, aquatic bivalve mollusks in the order Unionida.

The Mycetopodidae are a family of freshwater pearly mussels in the order Unionida restricted to South America. They are named for the mushroom-like shape of their foot. Like all members of the Unionida they reproduce via a larval stage that temporarily parasitizes fish. Banarescu lists four subfamilies with ten genera in total.