A less common but much more dangerous urchin is the flower urchin. The sharp spines of this creature are covered with a thin venomous skin which, if introduced into any wound can cause nausea, vomiting and swelling. Spines may also break off and remain embedded. Some species can give quite severe stings causing inflammation, swelling and pain lasting up to a week. Effects may sometimes be more severe.
Divers are particularly prone to brushing against hydroids.
They can be found in fairly shallow reef areas and on structures such as wharfs. Effects and treatment are similar to hydroid stings. It is normally yellowish brown but when disturbed its blue rings become bright and obvious. It is not aggressive by nature but will bite when provoked. The venom is contained in the saliva, which comes from two glands each as big as the animal s brain.