The colour in the mantle is algae; the clam farms them and lives largely on what they make.
Shell to about 40 cm, with rows of large fluted scales along the ribs and a wavy gape. The mantle displayed between the shell halves is patterned in blue, green, gold and brown, and the pattern is different in every individual. Several Tridacna occur here; T. squamosa is separated by the prominent scales, and T. crocea is smaller and bores into coral rock so that only the mantle is visible.
The mantle colour comes from symbiotic algae living in the tissue, which supply most of the clam’s food; the clam positions the mantle to expose them to light and filters plankton as a supplement. It closes when a shadow crosses it, which is why the first pass of a diver usually ends the photograph — approaching low and slowly, and waiting for the mantle to reopen, is the method. All giant clams are listed under CITES and have been heavily taken across the region. Recorded from about 1 to 20 m.
Ratings are per location: 1 means found on most dives that look for it, 5 means a handful of records. Where enough dives have been logged the figure is calculated from them; otherwise it is an editorial estimate, and says so. We publish habitat and destination, not the dive site.