Nurse sharksGinglymostomatidae

It does not chase anything. It pulls prey out of the reef with suction.

The mouth of a nurse shark is small and set well forward under a broad flat head, and behind it is a throat the animal can expand fast enough to drop the pressure inside its own mouth below the pressure of the water outside. Put that mouth over the opening of a crevice and the octopus wedged inside comes out whole. The suction a nurse shark generates is among the strongest measured in any fish, and it is applied with care rather than force: the shark will suck and spit the same mouthful several times, turning a crab end over end or working a shell loose before it swallows anything.

The rest of the animal is built around not needing to hurry. A pair of short fleshy barbels hangs beside the nostrils, which almost no other shark on this coast has, and it drags them over sand and rubble as feelers, testing holes it cannot see into. It also does not have to swim to breathe. It pumps water across its own gills while lying flat and motionless, which is how one of them spends an entire day parked under a ledge, often with others draped across it, and starts work only after dark.

The reputation for being harmless is mostly earned and comes with one caveat. A nurse shark will ignore a diver completely. A nurse shark that has been grabbed, sat on or pulled by the tail bites and then holds on, and the muscles that produce all that suction make it very difficult to get off again.

The family is small everywhere, and here it comes down to one species, the tawny nurse shark. It is not common in this sea, and it is an awkward animal to protect: slow, predictable, and findable in the same cave twice. It is listed as vulnerable across its range.