In this pit, a viscous secretion is exuded, entering the groove and hardening gradually upon contact with sea water. 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. It also serves as a fleshy anchor when the animal is stationary. 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 is used to pull the animal through the substrate (typically sand, gravel, or silt) in which it lies partially buried. In freshwater mussels, the foot is large, muscular, and generally hatchet-shaped. Like most bivalves, mussels have a large organ called a foot. 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). 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. Mussel shells carry out a variety of functions, including support for soft tissues, protection from predators and protection against desiccation. The valves are joined together on the outside by a ligament, and are closed when necessary by strong internal muscles (anterior and posterior adductor muscles). The mussel's external shell is composed of two hinged halves or "valves". Flight around a 3D- Rendering of a ♜T-Scan of a young Mytilus that is almost completely covered with Balanidae (barnacles). 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. General anatomy Marine blue mussel, Mytilus edulis, showing some of the inner anatomy. They are classified with the Heterodonta, the taxonomic group which includes most of the bivalves commonly referred to as "clams". Freshwater mussel species inhabit lakes, ponds, rivers, creeks, canals, and they are classified in a different subclass of bivalves, despite some very superficial similarities in appearance.įreshwater zebra mussels and their relatives in the family Dreissenidae are not related to previously mentioned groups, even though they resemble many Mytilus species in shape, and live attached to rocks and other hard surfaces in a similar manner, using a byssus. The common name "mussel" is also used for many freshwater bivalves, including the freshwater pearl mussels. The external colour of the shell is often dark blue, blackish, or brown, while the interior is silvery and somewhat nacreous. In most marine mussels the shell is longer than it is wide, being wedge-shaped or asymmetrical. A few species (in the genus Bathymodiolus) have colonised hydrothermal vents associated with deep ocean ridges. The word "mussel" is frequently used to mean the bivalves of the marine family Mytilidae, most of which live on exposed shores in the intertidal zone, attached by means of their strong byssal threads ("beard") to a firm substrate. These groups have in common a shell whose outline is elongated and asymmetrical compared with other edible clams, which are often more or less rounded or oval. Mussel ( / ˈ m ʌ s ə l/) is the common name used for members of several families of bivalve molluscs, from saltwater and freshwater habitats. A bed of blue mussels, Mytilus edulis, in the intertidal zone in Cornwall, England
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