The Alcyonacea, or the soft corals are an order of corals
which do not produce calcium carbonate skeletons. Instead they contain
minute, spiney skeletal elements called sclerites. Thus they are not
reef-building corals and do not lay new foundations for future corals.
One type is dead man's fingers, which is a type that is no larger than
7 centimeters and is found in warm water regions.
Unlike stony corals, most soft corals thrive in nutrient rich waters with less light intensity. Almost all contain and utilize zooxanthella as a major energy source. However, most will readily eat any free floating food, such as brine shrimp, out of the water column.
Soft corals are readily imported for the reef aquarium hobby.
However, becuase of their rapid growth under reef aquarium conditions,
aquacultured soft corals are preferred over wild collected specimens.
Often with a lower price and ussually hardier aquacultured specimens
are more practical.
Other organisms in the Alcyonaria subclass include sea pens, sea fans, sea whips and fleshy soft corals.
Information from Wikepedia - http://en.wikipedia.org/wiki/Alcyonacea