Photo copyright Tim Nicholson.
Soft Coral, Dendronephthya sp, taken in the Egyptian Red Sea.
Corals belong to a group of animals called Cnidarians. This includes hard and soft corals, sea fans, gorgonians, jelly fish and sea anemones. Amongst other common characteristics is the presence of stinging cells (nematocysts) which are used to catch prey.
A single coral animal is a polyp - the attractive "flowery" item looking like an anemone. The soft coral shown above is actually a colony of animals, each connected to its neighbour by living tissues. Soft corals are not reef-building, although they do secrete limestone. In their case this is as internal crystals called sclerites or spicules. Because soft corals do not have large skeletons, they grow faster than hard corals
Eight feathery tentacles surround the coral's mouth and whip food into it. They filter-feed: removing plankton from water flowing around the colony. Relatively recent data on soft corals indicates that they feed on very small planktonic particles, such as single-celled algae, rather than larger larvae as had previously been thought.
The Blue Planet, by Alastair Fothergill, Martha Holmes, Sir David Attenborough, BBC Consumer Publishing, 2001, ISBN 056-33-8498-0
The Red Sea in Egypt Part II, Invertebrates, by Farid S Atiya, Elias Modern Printing House, 1994, ISBN 977-00-6697-4