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.

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.

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.

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 sessile in areas of high flow.

Both marine and freshwater mussels are filter feeders; they feed on plankton and other microscopic sea creatures which are free-floating in seawater.

In some species, release occurs when a fish attempts to attack the mussel's mantle flaps, which are shaped like minnows or other prey, an example of aggressive mimicry.

[citation needed] Marine mussels are abundant in the low and mid intertidal zone in temperate seas globally.

[1] Other species of marine mussel live in tropical intertidal areas, but not in the same huge numbers as in temperate zones.

Certain species of marine mussels prefer salt marshes or quiet bays, while others thrive in pounding surf, completely covering wave-washed rocks.

The South African white mussel exceptionally does not bind itself to rocks but burrows into sandy beaches extending two tubes above the sand surface for ingestion of food and water and exhausting wastes.

Freshwater mussels inhabit permanent lakes, rivers, canals and streams throughout the world except in the polar regions.

[7] The seed is then typically reared in a nursery environment, where it is transferred to a material with a suitable surface for later relocation to the growing area.

After about three months in the nursery, mussel seed is "socked" (placed in a tube-like mesh material) and hung on longlines or rafts for grow-out.

For raft and longline culture, a platform is typically lowered under the mussel lines, which are then cut from the system and brought to the surface and dumped into containers on a nearby vessel.

Byssus threads secreted by the large Mediterranean pen shell, Pinna nobilis, which can be up to 6 cm (2.4 in) in length, have historically been made into cloth.

[12][13] The byssus of Atrina pectinata, a shell of the same family, has been used in Sardinia as a substitute for critically endangered Pinna nobilis, to weave sea silk.

[15][16] Further, mussel adhesive proteins inspired the design of peptide mimics that were well studied for surface bioengineering of medical implants.

Ongoing efforts in the Baltic Sea (Denmark, Sweden, Germany, Poland) and Long Island Sound[25] and Puget Sound[26] in the U.S. are currently examining nutrient uptake, cost-effectiveness, and potential environmental impacts of mussel farming as a means to mitigate excess nutrients and complement traditional wastewater treatment programs.

[35] In Belgium, the Netherlands, and France, mussels are consumed with French fries (mosselen met friet or moules-frites) or bread.

In Belgium, mussels are sometimes served with fresh herbs and flavorful vegetables in a stock of butter and white wine.

A similar style of preparation is commonly found in the Rhineland where mussels are customarily served in restaurants with a side of dark bread in "months containing an R", that is between September and April.

In the Netherlands, mussels are sometimes served fried in batter or breadcrumbs, particularly at take-out food outlets or informal settings.

In Italy, mussels are mixed with other seafood; they are most commonly eaten steamed, sometimes with white wine, herbs, and served with the remaining water and some lemon.

In Spain, they are consumed mostly steamed, sometimes boiling white wine, onion and herbs, and served with the remaining water and some lemon.

They are used in other sort of dishes such as rices or soups or commonly eaten canned in a pickling brine made of oil, vinegar, peppercorns, bay leaves and paprika.

In coastal Karnataka Bearys prepare special rice balls stuffed with spicy fried mussels and steamed, locally known as "pachilede pindi".

Mussels can be smoked, boiled, steamed, roasted, barbecued or fried in butter or vegetable oil.

As with all shellfish, except shrimp, mussels should be checked to ensure they are still alive just before they are cooked; enzymes quickly break down the meat and make them unpalatable or poisonous after dying or uncooked.