The Giant Clam

The Giant Clam is from the Tridacna gigas. T. gigas is one of the one of the most endangered clam species. It was mentioned in scientific reports as early as 1825. They live in shallow coral reefs and can weigh up to 441 lbs. They can also live as deep as 66 ft. They live in flat coral sand or broken coral. They are also found off the coast of the Philippines where they are called taklobo. Although larval clams are planktonic they become sessile in adulthood. The creatures mantle tissues act as a habitat for the symbiotic single-celled Dino Flagellate algae from which it gets its nutrition. By day the clam opens it’s shell and extends it’s mantle tissue so that algae receives the sunlight they need to photosynthesize. Young T. gigas are difficult to distinguish from other species of Tridacnidae. Adult T. gigas are the only clams unable to close they’re shells completely even when closed part of the mantle remains exposed. unlike the very similar T. derasa T. gigas have 4-5 folds in they’re shells unlike the T. derasa which has 6-7 folds. The largest known T. gigas specimen measured 137 cm it was discovered around 1817 on north-western coast of Sumatra the weight of the two shells was 230 kilograms 507 lbs this suggests that the live weight of the animal would have been roughly 551 lbs today these shells are on display in a museum in north Ireland today. Algae provides T. gigas with all supplement needed, in small clams 10 milligrams dry tissue weight filter feeding provide about 65% of total carbon needed for respiration and growth. Large clams 10 g acquire only 34% of carbon from this source. Legend as is often the case with uncharacteristically large species the giant clam has been historically misunderstood was known as “killer-clam” and “man-eating clam” and versions of the U.S. Navy Diving Manual even gave detailed instructions for releasing oneself from its grasp by severing the abductor muscles used to close its shell. In a colorful account of the discovery of the pearl of Lao Tzu, Wilburn Cobb said he was told that a Dyak diver was drowned when the Tridacna closed it’s shell on his arm. They also have thousands of tiny eyes all over them. They are not particularly good eyes, just good enough so that they can see a shadow pass over them so they can close they’re shell.

(Giant Clam)                                                                                                 (Pearl of Lao Tzu)