Cockles and True Cockle Shells of the Cardiidae Family
Ten Cockles and True Cockles Shells of the Cardiidae Family can be found in this website:
Phylogeny: Cockle Shells and True Cockle Shells of the Cardiidae Family are in the order Cardiida. Shells in this order are limited to marine environments. The Cardiida order consists of two superfamilies – Cardioidea and Tellinoidea. Cardiidae is the only family in the Cardioidea superfamily. Family Cardiidae is divided into nine subfamilies – Cardiinae with seven genera, Clinocardiinae with four genera, Fraginae with eight genera, Laevicardiinae with two genera, Lymnocardiinae with nine genera, Nemocardiinae with six genera, Orthocardiinae with four genera, Trachycardiinae with seven genera, and Tridacninae with two genera. There are two hundred seventy-two species in this family. Shells in the Cardiidae Family are also commonly known as Heart Shells because some have heart-shaped profiles.
Description: Cockle Shells are inflated and equivalve (both valves equal in size and shape) and they can be circular, trigonal or quadrate in shape. The shells can be thick, thin, or even translucent. The outside surface of the shell can be sculpted with fine to strong radial ribs or nearly smooth with fine commarginal striae. When present, the radial ribs can be scaly to spiny. The ribs may extend to the margin producing a serrated or scalloped edge. Most Cockle Shells are whitish, with varying amounts of brown or reddish banding or blotching. Their interiors are generally white and smooth. Unlike some bivalves, True Cockles can close their shells completely, with no gap around the edges. Living Cockle Shells have short siphons. The siphons of some species contain light receptors. The Cockle Shell’s foot is well developed, allowing it to move quickly across sand or mudflats. Most shells in this family are small to medium-sized, but the most famous members of the family are the Giant Clams (Genus Tridacna) from the Indo-Pacific that can reach a maximum of 1.5 meters (4 feet 11 inches) in length.
Habitat and Distribution: Cockles and True Cockles are generally found in sand and mud substrates. While considered marine species, some are found in brackish to fresh water. They may live in the intertidal zone, and to depths exceeding 500 m (1,640 feet). They have a global distribution in polar to tropical seas. Twenty species from this family are found in Mexican waters.
Natural History: Cockle and True Cockles are suspension feeders that filter plankton and fine detritus from the surrounding water. In turn they are preyed upon by birds, crabs, carnivorous mollusks and rays. They maybe gonochoric or simultaneous hermaphrodites. They reproduce sexually, through broadcast spawning, with external fertilization. Most species reach reproductive maturity when they are twelve months old and they generally have life-spans of between five and ten years. A startling exception are the Tridacna species which can live over one hundred years. Cockle Shells have been harvested as a food source and for use as a fishing bait since pre-historic times. Today, they are targeted by artisanal, recreational, and commercial fisheries. They are also raised in aquaculture farms in some regions.