Tridacna maxima is the smallest and most abundant of the four species of giant clams found in the Marshalls. On some reefs, you can easily spot hundreds of them embedded in the reef rock with their multicolored animals peeking out between the valves of the shell. They vary wildly in color, with no two exactly alike. Varying shades of green, blue, brown, and black are common; orange and lavender less so but still present. Some, like this one, are patterned with multiple pigments. One characteristic all Tridacna maxima seem to share, however, is the row of close-set black spots around the curving edges of the animal. The color of these clams comes from symbiotic zooxanthellae, a unicellular algae that lives within the tissue of the clam. The clam trades with the algae, giving up its waste products of carbon dioxide and possible some nutrients to the plant and getting in return products of the algae's photosynthesis, namely food and oxygen.