File:Mytilus sp. (mussels) (Yaquina Head, Oregon, USA) 1.jpg

English: Mytilus sp. - mussels in Oregon, 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 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.

Mussels are encrusting bivalves 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.

Seen here are mussel shells, Mytilus sp., along a rocky shoreline at Yaquina Head, Oregon. The rocks here are part of the Ginkgo Basalt, which is one of many lava flows in the Miocene-aged Columbia River Flood Basalt.

Classification: Animalia, Mollusca, Bivalvia, Pteriomorpha, Mytilida, Mytilidae

Locality: southern side of Yaquina Head, coastal Oregon, USA

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Info. at:

en.wikipedia.org/wiki/Mytilus_(bivalve)