File:Mytilus edulis (Atlantic blue mussel shells) (Bar Harbor, Maine, USA) 5.jpg

English: Mytilus edulis Linnaeus, 1758 - Atlantic blue mussel shells in Maine, USA.

Bivalves are bilaterally symmetrical molluscs having two calcareous, asymmetrical shells (valves) - they include the clams, oysters, and scallops. In most bivalves, the two shells are mirror images of each other (the major exception is the oysters). They occur in marine, estuarine, and freshwater environments. Bivalves are also known as pelecypods and lamellibranchiates.

Bivalves are sessile, benthic organisms - they occur on or below substrates. Most of them are filter-feeders, using siphons to bring in water, filter the water for tiny particles of food, then expel the used water. The majority of bivalves are infaunal - they burrow into unlithified sediments. In hard substrate environments, some forms make borings, in which the bivalve lives. Some groups are hard substrate encrusters, usually using a mineral cement to attach to rocks, shells, or wood.

The fossil record of bivalves is Cambrian to Recent. They are especially common in the post-Paleozoic fossil record.

Seen here are disarticulated Atlantic blue mussel shells, Mytilus edulis. This species occurs in much of the North Atlantic Ocean. Mussels are sessile, benthic, epifaunal, filter-feeding, hard substrate encrusters that are abundant in many intertidal rocky shore environments. They attach to substrates such as rockgrounds, hardgrounds, etc. by extruding byssus (a type of organic material), in the form of byssal threads.

Classification: Animalia, Mollusca, Bivalvia, Pteriomorphia, Mytiloida, Mytilidae

Locality: gravel/bedrock shoreline along Bar Harbor Shore Path, northeastern Mt. Desert Island, coastal Maine, USA (~vicinity of 44° 23’ 22.24" North latitude, 68° 12' 01.42" West longitude)

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See info. at:

en.wikipedia.org/wiki/Blue_mussel