Class Anthozoa

There are no medusal stages in this class which contains the corals, sea pens, sea fans and the sea anemones. There are around 6 500 recorded species worldwide, and most can be found in soft sediments. The size range for individuals is 1 mm - 10 m, though many seem much larger because they live in communities.

Anemones (see below left and right) range in size, with the largest being about ten centimetres in diameter and about twenty centimetres long. They attach to the substratum by a pedal disc. Some form mutualistic relationships with other animals, e.g. the hermit crab, where they are attached to the shell of the crab, but most live as solitary polyps. Urticina felicina, the dahlia anemone, below left, is found in waters below 22 ^oC, on the lower shore areas with strong wave action, although it can be found as deep as 200 m. Its tentacles are short and stubby, and usually arranged in multiples of 10. A fully mature species can have up to 160. With its tentacles it catches shrips, small fish, crabs, muscles, in fact anything it can. It can be up to 15 cm in diameter at the base, and 20 cm across the tentacles. Its colour is varaible. It can form dense carpets.

Many living corals look like miniature anemones. Instead of a pedal disc corals secrete a calcareous cup. These cups remain after death, and form coral reefs along with calcium carbonate precipitated from the symbiotic algae. Brain coral, Platygyra sp, below is found off the Queensland coast, Australia. It is a nocturnal carnivore which eats shrimps and plankton. It is a popular addition to many aquariums. Deep sea trawling is the greatest threat to cold water corals. In a 2 week trawling trip the average trawler sweeps over 33 km² of sea bed.

Sea fans grow so that their flat surface faces the current, see Melitodes virgata on the right. Their tentacles strain food particles out of the passing water. Some sea fans in colder waters can have colonies as high as 5 m, and look like underwater forests.

Sea pens get their name because they look like old-fashioned quill pens, see Pennatula phosphorea above left. It is found in the NE Atlantic and the Mediterranean, usually in waters more than 10 m deep, and is usually in colonies. It grows up to 25 cm long and as its name suggests it can luminesce when disturbed.