These black needle urchins are armed with spines, which they wave menacingly at intruders. Although they look sinister, they eat algae which they graze off the rocks.
The spines are hollow and can pierce flesh easily. They contain a toxin which causes a stinging sensation. You definitely do not want to stand on one of these!
Treatment of venom
If you do happen to stand on a needle urchin or have your hand pierced by a spine, immediately put the inflicted area into hot water (as hot as you can stand without being burnt!). This will destroy the protein-base of the toxin and will relieve the pain. Seek medical advice to prevent secondary infection, or if there is a risk of respiratory or cardiac failure.