monomyarianism

mollusk anatomy

Written by

The Information Architects of Encyclopaedia Britannica

Last updated

June 30, 2026

Quick Summary

Monomyaria is a classification of bivalve mollusks that are characterized by having only one adductor muscle. This is in contrast to dimyarian bivalves, which have two adductor muscles. Examples of monomyarian bivalves include oysters and scallops. This anatomical feature is a result of evolutionary changes in bivalve musculature, where the anterior adductor muscle has been reduced or lost, leaving the posterior adductor muscle as the primary one for closing the shell. This adaptation is often associated with bivalves that are cemented to a substrate or have a more radial symmetry in their shell structure.123

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

6 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
Internal features
…creates what is called the monomyarian condition. In bivalves with such a configuration, the anterior shell and mantle are confined to a small area; the foot, where present, is always greatly reduced and positioned anteriorly. The visceral mass and organs of the mantle cavity are arranged around the central posterior…
Read More
…creates what is called the monomyarian condition. In bivalves with such a configuration, the anterior shell and mantle are confined to a small area; the foot, where present, is always greatly reduced and positioned anteriorly. The visceral mass and organs of the mantle cavity are arranged around the central posterior…
Read More