Editing Mussel (section)

==General anatomy==
[[File:Miesmuscheln-2.jpg|thumb|left| Marine [[blue mussel]], ''Mytilus edulis'', showing some of the inner anatomy. The white posterior adductor muscle is visible in the upper image, and has been cut in the lower image to allow the valves to open fully.]]
 	
[[File:3D flight around a µCT scan of a Mytilus covered with Balanidae.ogv|thumb|300px|right|Flight around a 3D-[[3D rendering|rendering]] of a [[Computed tomography|μCT]]-scan of a young [[Mytilus (bivalve)|Mytilus]] that is almost completely covered with [[Balanidae]] (barnacles). Resolution of the scan is 29&nbsp;μm/[[Voxel]].]]

The mussel's external shell is composed of two hinged halves or "valves". The valves are joined on the outside by a ligament, and are closed when necessary by strong internal muscles (anterior and posterior adductor muscles). Mussel shells carry out a variety of functions, including support for soft tissues, protection from predators and protection against desiccation.

The shell has three layers. In the pearly mussels there is an inner iridescent layer of [[nacre]] (mother-of-pearl) composed of [[calcium carbonate]], which is continuously secreted by the mantle; the prismatic layer, a middle layer of chalky white crystals of calcium carbonate in a protein matrix; and the [[periostracum]], an outer pigmented layer resembling a skin. The periostracum is composed of a protein called [[conchin]], and its function is to protect the prismatic layer from abrasion and dissolution by acids (especially important in freshwater forms where the decay of leaf materials produces acids).

Like most bivalves, mussels have a large organ called a [[Foot (mollusc)|foot]]. In freshwater mussels, the foot is large, muscular, and generally hatchet-shaped. It is used to pull the animal through the substrate (typically sand, gravel, or silt) in which it lies partially buried. It does this by repeatedly advancing the foot through the substrate, expanding the end so it serves as an anchor, and then pulling the rest of the animal with its shell forward. It also serves as a fleshy anchor when the animal is stationary.

In marine mussels, the foot is smaller, tongue-like in shape, with a groove on the ventral surface which is continuous with the byssus pit. In this pit, a viscous secretion is exuded, entering the groove and hardening gradually upon contact with sea water. This forms extremely tough, strong, elastic, byssal threads that secure the mussel to its substrate allowing it to remain [[Sessility (motility)|sessile]] in areas of high flow.<ref>{{Cite journal|last1=Vaccaro|first1=Eleonora|last2=Waite|first2=J. Herbert|date=2001-09-01|title=Yield and Post-Yield Behavior of Mussel Byssal Thread: A Self-Healing Biomolecular Material|journal=Biomacromolecules|volume=2|issue=3|pages=906–911|doi=10.1021/bm0100514|pmid=11710048|issn=1525-7797}}</ref> The byssal thread is also sometimes used by mussels as a defensive measure, to tether predatory molluscs, such as [[dog whelk]]s, that invade mussel beds, immobilising them and thus starving them to death.

In cooking, the [[byssus]] of the mussel is known as the "beard" and is removed during preparation, often after cooking when the mussel has opened.

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