Bivalvia – Mussels

The Bivalvia are a class in the phylum of the Mollusca which cotains about 8000 species. Mussels are also known as Acephala, Cormopoda, Lamellibranchia and Pelecypoda.


Mussels have a reduced head compared to other molluscs. The laterally compressed, soft body is enclosed and protected on both sides by the mantle. The mantle also produces the shells, which consist predominantly of calcium carbonate. The shells are movably connected at the base with a ligament.

Some species have eyes at the edge of their mantle. In most of them, these are primitive and serve only the distinction between light and dark. However, some have lens eyes with which they can perceive movements and presumably also contours.

Bivalvia have a foot, which is largely degenerated in fixed and floating species. However, there are also species that are able to move.

Habitat and Distribution

Mussels are found in salt water, as well as in brackish and fresh water. They are found from the polar regions to the tropics. Most of them are between 0 and 100m, but there are species that are as much as 11000m deep.

As adult animals the larger part of the Bivalvia lives sessil, whether on firm ground or in the sand.


Originally, Mussels were sediment eaters. Out of this plankton feeder and specialized eating behaviours resulted. There are for example wood eaters, hunters and bacteria cultivator.

Many highly developed mussels feed only by filtering their breathing water and eat almost exclusively plankton. As a result, they come into contact with large amounts of water, which makes them excellent bioindicators. This means that they can be used to measure exposure to specific environmental factors.

Few specialized species actively chase small creatures through sucking.

Bivalvia from the subfamily Tridacna and the genus Solemya live symbiotically with algae, which are located in the mantle edge. By this they are supplied with organic material and oxygen.

Species of Bivalvia on the Canary Islands