A cockle is a bivalve mollusk of the family Cardiidae, of which there are over 200 living species. Many species of cockles are popular in European and Asian cuisines. Empty cockle shells are ubiquitous on beaches around the world, and many find them attractive. As with all bivalves, the shells have two symmetrical sides. Cockle shells are round and distinctively ridged.
Cockles have a foot with which they can burrow and leap briefly out of the water. They are filter feeders that subsist on plankton. The cockle is one of the fastest reproducing bivalves, due to its hermaphroditism. Each cockle can function as either sex, meaning that any two can reproduce.
Cockles have a vast native range spanning the coasts of much of Europe, North Africa, and East and Southeast Asia. In addition to the 200 living species, there are many other species in the fossil record. Cockles are harvested from the beach at low tide, which is a grueling and potentially dangerous job.
Cockles are traditionally eaten in many areas of the world. In the United Kingdom, cockles are popular pickled or fresh with vinegar. Cockles are the centerpiece of many Asian dishes as well. They are also sometimes used as bait for marine fish. Eating raw cockles can be dangerous, as they have been linked to hepatitis.
In English, the slang phrase "the cockles of my heart" is used to refer to the ventricles, typically in an expression of delight, such as, "That music warms me to the cockles of my heart." This is possibly because the two sides of a cockle shell resemble a heart shape, though linguistic explanations have also been posited. The Latin diminutive of the word meaning "heart" is corculum, while the Latin name of the ventricles is cochleae cordis, literally "snails of the heart." Cockles also appear in a few English language folk songs and nursery rhymes, such as "Molly Malone" and "Mary, Mary, Quite Contrary."