What is "tridacna"

Tridacna \Tri*dac"na\, n. [L., pl., a kind of oysters, fr. Gr. ? eaten at three bites, ? tri- + ? to bite.] (Zo["o]l.) A genus of very large marine bivalve shells found on the coral reefs of the Indian and Pacific Oceans. One species ( Tridacna gigas) often weighs four or five hundred pounds, and is sometimes used for baptismal fonts. Called also paw shell, and fountain shell.

n. Any member of the genus (taxlink Tridacna genus noshow=1) of large saltwater clams with heavy fluted shells.

Tridacna is a genus of large saltwater clams, marine bivalve mollusks in the subfamily Tridacninae, the giant clams. They have heavy shells, fluted with 4 to 6 folds. The mantle is brightly coloured. They inhabit shallow waters of coral reefs in warm seas of the Indo-Pacific region. These clams are popular in marine aquaria, and in some areas, such as the Philippines, members of the genus are farmed for the marine aquarium trade. They live in symbiosis with photosynthetic algae ( zooxanthellae). Some species are eaten by humans.