CorallimorphariaCorallimorpharia

A corallimorph is a stony coral that does not make the stone. Same order of animal, same mouth in the middle of a ring of tentacles, and in most of them the same algae living in the tissue, but there is nothing hard underneath: the whole polyp is a soft disc pressed flat to the rock. Molecular work suggests they descend from skeleton builders that gave the skeleton up, which is why the group gets called the naked corals.

They are the animals nobody can put a name to underwater, because they sit exactly between a coral and an anemone. The disc is what tells them apart. A corallimorph is a lid: flat, round, wider than the short column beneath it, with the tentacles reduced to knobs, warts or rows of beads scattered across the whole surface instead of a fringe of long arms around a mouth. An anemone sits alone with its column wedged into a hole in the reef. A corallimorph spreads as a sheet of identical discs, identical because they are all the same animal split up again and again.

The largest one here is worth recognizing. The elephant ear grows into a shallow bowl with a pale collar around the rim, and small fish treat the bowl as shelter, which is the point of it. When one settles inside, the disc folds shut over the fish like a purse being pulled tight, and it is digested inside the fold. Divers who lay a hand flat on one describe the same thing happening to the hand.

Where they take ground they keep it. Corallimorph carpets grow out across dead coral and rubble and hold the space against anything trying to settle on it, and on damaged reefs elsewhere in the world these mats have taken over ground that used to be coral and stayed for years. On a healthy reef in this sea they are simply one of the ordinary sights of the shallows, in brown, green, purple and occasionally blue.