Mytiloida Mytilida is an order of marine bivalve molluscs, commonly known as true mussels.

Species in the order Mytilida 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.

Mytilids include the well-known edible sea mussels.

The animals attach themselves to a solid substrate using a byssus.

In 2010, a new proposed classification system for the Bivalvia was published by Bieler, Carter & Coan.