The Mytilidae are a family of small to large saltwater mussels, marine bivalve mollusks in the order Mytiloida. One of the genera, Limnoperna are inhabits in brackish or freshwater environments. The order has only this one family which contains some 52 genera. Species in the family Mytilidae are found worldwide, but they are more abundant in colder seas, where they often form uninterrupted beds on rocky shores in the intertidal zone and the shallow subtidal. The subfamily Bathymodiolinae is found in deep-sea habitats. Mytilids include the well-known edible sea mussels.