Whiptail stingrayDasyatidae

The sting is a tooth. It is a dermal denticle, the same structure as the scales that make a ray's skin rough, grown long and flat and mounted on the top of the tail, with backward-pointing serrations along both edges and a shallow groove running down each face. Venom-producing tissue sits in those grooves under a thin sheath of skin. Nothing is injected under pressure: the sheath tears as the spine goes in, and the venom goes in with it.

The spine points backward, which tells you what it is for. A stingray cannot use it on anything in front of it. The strike is a whip of the tail up and over the animal's own back, aimed at whatever has come down on top of it, and in practice that is a foot. People are stung in the shallows, standing on a buried ray they never saw. Divers hovering over one are looking at an animal that would much rather leave. Shuffling your feet through the sand instead of stepping down is the whole of the prevention.

The wound is worse than a puncture, because the serrations tear on the way back out and fragments of sheath and denticle stay behind. The venom is protein and heat breaks it down, so the standard treatment is to put the limb in water as hot as it can be borne without scalding and keep it there while help is arranged. The pain drops within minutes; the wound still needs cleaning, checking for retained fragments and antibiotics, and infection is what usually causes the trouble afterward. Deaths are rare and involve the chest or the abdomen rather than a limb.

Everything else about this family is mild. These are the rays divers actually meet on this coast, from a bluespotted ribbontail the size of a dinner plate wedged under a coral head to a blackblotched stingray close to two meters across lying on open sand with the edges of its disc rippling. The tails run whip-thin, several times the length of the animal in some species. The spine breaks off and grows back, and the ray has no interest at all in spending it on you.