The Bluegreen Giant Clam (Tridacna derasa) is a marine (saltwater) reef bi-valve mollusc in the Cardiidae family. It is also called the Southern Giant Clam. It is related to the Cockle.
The Bluegreen Giant Clam is smoother than most clams, because it lacks ridging. It has a thick shell, called a mantle. Its shell is actually two equal-sized calcareous valves connected with a flexible adductor muscle. The shell can open and close. Bi-valve means two valves (or two shells). It has 6-7 rippled edges, called folds or flute. It does not have scutes (scales). The mantle has stripes or spots and is blue and green, with some white patches. It has a mouth, a heart, kidneys, a stomach, and a nervous system.
It measures up to 60 centimetres (24 inches) in length.
The Bluegreen Giant Clam is native to the oceans around Australia, Cocos Island, Fiji, Indonesia, New Caledonia, Papua New Guinea, the Philippines, and north to Vietnam. It prefers the outer edges of coral reefs.
It is a filter feeder. It feeds on microscopic aquatic algae that live within it and near it. It has a mouth. It opens its shell during the day and closes its shell at night. The shell can shut completely.
It breathes though gills (like fish).
The Giant Clam is hermaphroditic, meaning that it has both male and female reproductive organs, and can produce eggs and sperm. It releases about 500 million eggs at a time – fish eat most of them.
After 12 hours, the eggs hatch into larvae, called trocophores. The larvae produce a calcium carbonate shell. It moves along the sea bed using its newly-developed foot. It can also swim. After about one week, the Giant Clam settles on the ocean floor and becomes sessile – the foot disappears and it cannot move.
Photographer: Martina Nicolls
Martina Nicolls: SIMILAR BUT DIFFERENT IN THE ANIMAL KINGDOM