A clam: made of light and all the while afraid of the dark | Helen Sullivan

The height of solar efficiency, a clam manipulates light to make its shell and redirects the sun's rays to its tiny algal tenants

A giant clam has hundreds, if not thousands, of eyes, which lie on the exposed flesh that lines the shell, and work like pinhole cameras. They respond by withdrawing the mantle to movements of dark objects, even if these cast no shadow on the animal as a whole," reads one description. They also tell the clam to close when the light dims or changes direction. I read this and imagine the dark shape of a scuba diver scanning her torch across the curves of the clam's mouth. Depending on how deep or shallow these curves are, the clam looks happier or angrier.

There are many species of giant clam. The Latin name of one kind, commonly found in the waters around Indonesia, Palau and Vanuatu, is Hippopus hippopus. Giant clams are about as wide as a short woman is tall. Their muscle, or flesh (the part of them that is alive), is only a fraction of their weight. Dead, the largest giant clam recorded weighed only 20kg less than it weighed alive: 250kg. The heaviest weighed 340kg alive, and 333kg dead. (By comparison, the human skeleton weighs between 1.5kg and 3.5kg.) They are so heavy they don't need to attach themselves to the sea bed. Their pearls don't shine - there is no spare light.