Myida

Myida (formerly Myoida) is an order of saltwater and freshwater clams, marine and freshwater bivalve molluscs in the subclass Heterodonta. The order includes such bivalves as soft-shell clams, geoducks and shipworms.

Description
They are burrowing molluscs with well-developed siphons. The shell is relatively soft and lacks a nacreous layer. Some species have a single cardinal tooth.

Superfamilies and families
Superfamilies and families within the Myida include:


 * Superfamily: Dreissenoidea
 * Family: Dreissenidae
 * Superfamily: Myoidea
 * Family: Corbulidae
 * Family: Myidae
 * Family: †Pleurodesmatidae
 * Family: †Raetomyidae
 * Superfamily: Pholadoidea
 * Family: Pholadidae
 * Family: Teredinidae
 * Family: Xylophagaidae
 * Superfamily: †Pleuromyoidea
 * Family: †Ceratomyidae
 * Family: †Pleuromyidae
 * Family: †Vacunellidae