The giant clam that lives nowhere else. Endemic to this sea and the 🌊 Gulf of Aden, it sits on shallow reef tops with its mantle spread to the light, patterned in blue, green or brown, and closes with a slow deliberate movement when a shadow crosses. Six or seven deep radial folds in the shell separate it from its commoner relatives, which have four to six.
Like all giant clams it farms rather than hunts. Symbiotic algae live in the mantle tissue and hand over most of the sugars they make, which is why the animal spreads that mantle in full sunlight and why it cannot live deep. Filtering plankton makes up the difference, but the light is the main meal.
Rarity here is not an accident of nature. The species was described in 1899, then effectively lost for most of a century - long treated as an odd form of another clam - and only confirmed as its own species again in the 2000s. By then it had been fished out of most of its range for meat and shell. Surveys now find it in single figures at sites where it should be ordinary, which makes every individual worth leaving exactly where it is.
- six or seven deep radial folds in the shell, against four to six in other local giant clams
- mantle patterned in blue, green or brown, filling the gape
- sits free on the reef top rather than buried in coral
- shell to 34 cm
