Alex Mustard / Backlit detail of branching fire coral (Millepora alcicornis) showing the hair like polyps, filled with stinging nematocysts. East End, Grand Cayman, Cayman Islands. Caribbean Sea.

Juergen Freund / Box jellyfish {Chiropsalmus sp.} in fishtank on beach with palmtrees in background, Queensland, Australia

Juergen Freund / Box jellyfish {Chironex sp.} in mangroves, split level, Australia

Sue Daly / Colony of Sunset cup corals (Leptopsammia pruvoti), Sark, British Channel Islands, UK, July.

Sue Daly / Close-up of a Sunset cup coral (Leptopsammia pruvoti), with tentacles moving, Sark, British Channel Islands, UK, July.

Sue Daly / Colony of Sunset cup corals (Leptopsammia pruvoti), Sark, British Channel Islands, UK, July.

Sue Daly / Snakelocks anemone (Anemonia viridis) moving in the current, Sark, British Channel Islands, UK, June.

Sue Daly / Group of Jewel anemones (Corynactis viridis), Sark, British Channel Islands, UK,

Sue Daly / Yellow cluster anemones (Parazoanthus axinellae) with a Bloody Henry starfish (Henricia oculata), Sark, British Channel Islands, UK, August.

Sue Daly / Group of White-striped anemones (Actinothoe sphyrodeta), with tentacles moving in the current, Sark, British Channel Islands, UK, July.

Alex Mustard / Backlit photo of stinging nematocysts on colony of Fire coral (Millepora dichotoma) Gubal Island, Egypt. Strait Of Gubal, Red Sea.

Pete Oxford / Fire Coral (Millepora alcicornis) with fine hairs that contain nematocysts which sting on contact, Belize Barrier Reef, Belize