Home Page of the phylum Cnidaria, the major group of invertebrates that includes the sea anemones, corals, jellyfishes, hydroids, and animals that contain 'cnida' stinging capsules.
Compass Jellyfish, Chrysoara hysoscella
Greek knide = nettle
Radially symmetrical animals with a simple form, all with stinging capsules. These capsules are activated when chemically or mechanically stimulated. Species appear as polyps (sea anemones) or medusa (jellyfish), and often a species goes through both forms in its life cycle (jellyfish, hydroids). Cnidarians live in the sea except for a few (e.g. hydra) that inhabit fresh water.
Class Zoantharia (Hexacorallia): Corals, Sea Anemones.
The stinging capsules in the tentacles and other parts of the sea anemone are called cnidae. The commonest type are called nematocysts. These capsules can be seen under the microscope and their mechanism is arguable the fastest action in the whole of the animal kingdom. The fluid filled capsule called the nematocyst everts and forces the filament to discharge venom into its prey of smaller organisms.
Worldwide Cnidaria Web Site
The Sea Fan, Swiftia pallida, is found in the cold Scottish seas.
The slender arms provide
the base for a single species of sea anemone in British waters.
More information on this discovery (link)
IMAGES on flickr
Cnidaria of the NE Atlantic on facebook
of British Cnidarians
Cnidarians of the World