Anthozoans (Class: Anthozoa)
Occurrence - Worldwide; on the sea bed, in soft sediments.
The word “anthozoa” means “flower animal”, and with their bright colours, waving tentacles, and fleshy trunks, these animals often look remarkably like plants. However, they are carnivorous - as are all cnidarians - although some species supplement their diet with food produced by microscopic algae harboured in their bodies. Anthozoans vary greatly in size, ranging from minute species less than 1mm across, to those over 10m across. When adult, they form polyps - simple, tubular animals with the tube closed at one end and open at the other. The open end is drawn out into one or more whorls of tentacles containing stinging cells, used for feeding and for defence against predators as varied as gastropods, polychaetes, sea spiders, and starfish. Anthozoans multiply asexually and sexually. Many species are solitary, but this group also includes colony-forming hard corals - animals that are responsible for building coral reefs, the biggest structures in the living world. These are formed by the animals’ external calcareous skeleton. Other widespread anthozoans include soft-bodied sea anemones, plus sea pens and sea fans that have flexible, horny internal skeletons.