Giant Clam

The giant clam, scientifically Tridacna gigas, is the best-known species of the giant clam genus Tridacna and the largest living bivalve mollusc, native to the shallow coral reefs of the Indo-Pacific, including the South China Sea and waters off the Philippines. Individuals may weigh more than 200 kilograms, measure as much as 120 centimetres across and live for over a century in the wild, and the species has been known to the indigenous peoples of East Asia for thousands of years, with the Venetian explorer Antonio Pigafetta documenting it in a journal as early as 1521. Though its larvae are free-swimming, the giant clam becomes permanently fixed in place as an adult, and its mantle tissue hosts symbiotic algae from which it derives most of its nutrition, opening its shell by day so the algae can photosynthesise, a relationship now studied as a model for efficient bioreactors. Populations have declined sharply across much of the giant clam's range and it has disappeared entirely from many areas where it was once common.