Most dangerous sea urchin

The flower urchin (Toxopneustes pileolus) of the Indo-Pacific region is widely regarded as the most dangerous sea urchin. Venom delivered by the pedicellaria (small pincer-like organs) that cover the urchin's hard shell (test) can cause contractions in smooth muscle which lines many major organs, including cardiac (heart) tissue. This can lead to severe pain, respiratory problems and even paralysis. Although there have been reported fatalities of swimmers who have drowned after being stung by these urchins, none have been scientifically verified to date.

The genusToxopneustes contains four species, all of which possess similarly severe toxins; the fact that T. pileolus is the most widespread also adds to the threat that it poses.

The active chemical in the flower urchin's venom that causes such a severe reaction is a glycoprotein called Contractin A.

There have been surprisingly few studies done into sea urchin venom to date. One historical account from 1935 in Annotationes Zoolgicae Japonenses reveals what it feels like to be stung by a flower urchin, as told by Dr Tsutomu Fujiwara of the Hiroshima Zoological Laboratory in Japan:

On June 26, 1930, while I was working on a fishing boat on the coast of Tsuta-jima in Saganoseki, I scooped up with my bare hand an individual of the sea-urchin which had been carried up by a diver with a fishing implement on the water surface from the sea-bottom about 20 fathoms in depth, and I transferred the sea-urchin into a small tank in the boat. At that time, 7 or 8 pedicellariae stubbornly attached themselves to a side of the middle finger of my right hand, detached from the stalk and remained on the skin of my finger.

Instantly, I felt a severe pain resembling that caused by the cnidoblast of Coelenterata, and I felt as if the toxin were beginning to move rapidly to the blood vessel from the stung area towards my heart. After a while, I experienced a faint giddiness, difficulty of respiration, paralysis of the lips, tongue and eyelids, relaxation of muscles in the limbs, was hardly able to speak or control my facial expression, and felt almost as if I were going to die. About 15 minutes afterwards, I felt that pains gradually diminish and after about an hour they disappeared completely. But the facial paralysis like that caused by cocainization continued for about six hours.