COCKLE, a bivalved marine mollusc of the genus Cardium, allied to the oyster and placed in the class Lamellibranchia. About 200 living species of cockles are known and over 33o fossil forms have been described. The common or edible cockle (Cardium edule) is the best-known example and is of some economic impor tance.
The two valves of the shell of the cockle are similar and are characterized by a prominent umbo (see LAMELLIBRANCHIA) from which a number of prominent ribs radiate over the surface of the shell. The animal has a long and pointed foot with a knee-like bend in it. The mantle is produced into two short "siphons" which bear numerous finger-like processes. In certain species these processes carry eyes at their tips. The cockle is placed in the order Eulamellibranchiata.
The cockles live on the sea-bottom and are usually found buried below the surface. The common cockle, and probably most of the other species, rarely penetrates below one inch from the surface. The muscular, pointed foot enables it to dig into and plough its way through sand and mud. It has a moderately wide range of habitat, but is rarely found on any soil other than sand and mud. Wright states that Cardium edule thrives best in estuarine waters, where the salinity is a little less than that of normal sea-water. Cockle beds formed on the open coast are rarely permanent. In water of high or very low salinity the shell is subject to certain peculiar modifications (Bateson : George). The cockle, like the rest of the Lamellibranchia, has no organs of mastication. It feeds on minute animals and plants and on the organic particles found in sea-water. The spores of Algae, Foraminifera, Diatoms, etc.
usually constitute its diet. The animal is a "current feeder," the food being drawn into the branchial chamber in the water currents produced by the lower siphon. In England and Wales the most important cockle-fisheries are in the Thames estuary, the Wash, Carmarthen and Morecambe Bays. The animals are gathered by hand or by various kinds of rakes and scrapers and are boiled (in certain places by special methods to ensure the destruction of typhoid bacilli) before being despatched to market. In 19 2 5, 300, 2 2 I cwt. of cockles were landed in England and Wales. The nutritional value of the common cockle is fairly high, though its tissues contain less protein and fat than those of the oyster and mussel.
See E. Romer, "Cardium" in Kiister's Conchylien Cabinet (vol. K. 1869) ; J. Johnstone, Cardium (Liverpool Mar. Biol. Committee Memoir, 1899, bibl.) ; F. Wright, Fishery Investigations (Ministry of Agriculture and Fisheries, ix. 5, 1926, bibl.) . (G. C. R.)