Not all stingers are large and obvious. Quite a few molluscs have stinging mechanisms, such as nudibranchs, which eat stinging hydroids and anemones and can store the nematocists of their prey in their own tentacles for defence against predators. Sea urchins and starfish are the last and most obvious group of marine creatures lurking to catch unwary and clumsy humans. The spines of a number of sea urchins can be poisonous and, even if not, can puncture the skin through gloves, leaving painful wounds which can go septic. As they are made of calcium, any such spines should dissolve after a few days, though deeply embedded ones can leave permanent scarring and patients may have to be treated for shock.
Treatment includes rubbing with the juice and pulp of the paw paw fruit.
Another sea urchin to watch out for, particularly in the Red Sea, where it is very common on deep reefs and in the shaded areas of wrecks, is Asthenosoma varium. Divers should beware of them when diving inside wrecks, as exhaled bubbles can dislodge them. The starfish will then roll into a tight ball, spines on the outside, and if it lands on you, those spines can easily penetrate a wetsuit and dig into the skin.