■Octopus

Octopi, particularly large ones, have such powerful suckers that they present the danger of freely manipulating and injuring a diver, such as taking hold of the diver’s mask or regulator.
The tiny and beautiful blue-ringed octopus possesses a poison so toxic that one bite is deadly. However, these are not aggressive unless provoked.

■Jellyfish

Most jellyfish possess poisonous nematocysts in their tentacles. The Portuguese man-of-war and similar jellyfish are deadly.

■Cone Shell

The attractive and seemingly innocuous cone shell is has a powerful poisonous needle that darts out when disturbed, to deadly effect.

■Sea Urchin

Diadem urchins (longspine urchins) and other sea urchin have poisonous spines which easily penetrate wetsuits and skin before breaking off to remain imbedded underneath the skin. Iijima Fukuro urchins and pacific urchins possess neurotoxins – keep clear!

Diadem urchins
(longspine urchins)

Iijima Fukuro urchins

■Crown of Thorns Starfish

Living on coral reefs, these starfish possess wide, pointed, poisonous thorns. Since they have had an explosive increase in population in recent years, these coral, coral crab and conch shell-eating pests are now targeted as a protective measure.

■Hydrozoan Stinging Ferns

With branches resembling chicken feathers, these hydrozoans (in the same family as jellyfish) have nematocysts which, when brushed up against, fire. The result is a pricking pain, ache, red blisters and strong itchiness lasting several days.

■Fire Coral

Very similar to regular coral reef, these are widely distributed among tropical reefs. If accidentally touched, these produce a burning pain and inflammation that lasts for several days.