It turns out that this mollusk’s boring organ is anything but
Nhobgood/Wikimedia Commons (CC BY-SA 3.0)
Burrowing giant clams have perfected the ship-in-a-bottle trick, and the one big thing that scientists convinced themselves couldn’t explain it, actually can.
Tridacna crocea, the smallest of the 10 or so giant clam species, grows a shell that eventually reaches the size of a large fist. Starting as youngsters, the burrowers bore into the stony mass of an Indo-Pacific coral reef, trapping themselves behind a too-skinny exit for their entire decades-long lives.
Only the extravagantly colored upper edges of the clam’s body can push out the thin slit in the reef. These protruding frills teem with algae related to those in corals. Basking in sunlight, the algae pay rent in the form of a substantial portion of a giant clam’s nourishment.
The clams “actually have eyes in this tissue,” says environmental physiologist Richard Hill of Michigan State University in East Lansing. At the slightest shadow — a predator, perhaps —