These are the second most primitive animals after the sponges. The cnidarians have a very simple construction, but contain some internal organs as well as a primitive neural system.

Cnidarians come in many sizes but basically only in two shapes. Either as benthic polyps that look like flowers or pelagic medusa that look like parachutes. Many species go through both of these stages during their life.

The best known cnidarians are planktonic jellyfish. They do in fact also occur as benthic polyps for part of their life, but when mature change over to the pelagic medusa stage. This usually happens in late summer and autumn.

Well know benthic groups are corals, sea anemones and hydrozoans. Corals and sea anemones are closely related, but differ, mainly because corals are colonies of very small individuals, while sea anemones are large solitary individuals. Corals are usually associated with the tropics, but coral reefs also occur in deep waters in colder areas of the oceans, including Icelandic waters.

Cnidarians are all predators that eat whatever reaches their tentacles and they can handle. The tentacles are covered with cells, called namatocysts that can inject venom into prey or potential predators. Cnidarians should therefore be handled with care. Icelandic species do not kill people but can cause rashes or even burns on the skin. Some species in warmer waters can be lethal.

Cnidarians are not harvested in the North Atlantic. However, in the Far East some species are harvested and eaten.

HV

Various cnidarians, sea anemones and hydrozoans on the bottom, Arctic liona mane jellyfish floating by (photo: Erlendur Bogason) Various cnidarians, sea anemones and hydrozoans on the bottom, Arctic liona mane jellyfish floating by (photo: Erlendur Bogason)