Myoida

bivalve order

Written by

The Information Architects of Encyclopaedia Britannica

Last updated

July 1, 2026

Quick Summary

The Myoida are an order of bivalve mollusks. These marine animals are characterized by their ability to burrow deeply into sediment or bore into rock and wood. Myoida typically have thin shells that are equivalve (both shells are the same size and shape) and often possess long siphons that extend to the surface for respiration and feeding. Their hinge structure is often degenerate, and they may develop accessory shell plates to aid in boring. This order includes families like the Myidae and Pholadidae.12

Summary created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

2 Britannica Sources

Ask Britannica AI about this topic

Britannica doesn't have a full article on this topic, so we've curated a list of our relevant coverage.

bivalve
Annotated classification
Order Myoida Shell typically thin, equivalve, comprising either 2 or 3 layers; hinge plate with cardinal dentition, often degenerate; approximately isomyarian but with much variation; boring forms develop accessory shell plates; ctenidia eulamellibranch, mantle margins extensively fused and covered in periostracum; small foot; marine deep burrowers…
Read More
Order Myoida Shell typically thin, equivalve, comprising either 2 or 3 layers; hinge plate with cardinal dentition, often degenerate; approximately isomyarian but with much variation; boring forms develop accessory shell plates; ctenidia eulamellibranch, mantle margins extensively fused and covered in periostracum; small foot; marine deep burrowers…
Read More