Animal of the Week February 28, 2005 -- Giant Clam

This week's animal of the week is Tridacna gigas (giant clam). These tropical bivalves are the heaviest of all the molluscs (mysterious/fictional giant squid notwithstanding), they grow up to 1.3 m across and can weigh up to 250 kg (that's 4'4" and 550 lb for our imperial American friend). Although depicted in many an adventure story trapping the foot of a happless pearl diver, there is not a single documented case of someone being drowned by a giant clam, indeed some of the largest ones can't close there valves fully. Instead of dining on divers extremities, giant clams obtain most of their food from symbiotic algae (zooxanthellae), although Tridacna gigas does obtain some (~10%) of it's nutrients by filtering phytoplankton and zooplankton from sea water. These clams live in shallow coral seas and are found no deeper than 20 m below the surface. They breed by ejaculating vast numbers of eggs and sperm into the sea, which makes me wonder about the diver in this week's picture.