Appearance and lifestyle:
Needle urchins (Diadema setosum) are armed with spines, which they wave menacingly at intruders. 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.
Habitat:
They are found in shallow and mid depths waters on coral and rocky reefs.
Diet:
They eat algae which they graze off the rocks.
Threats:
Overcollection, pollution, climate change etc.