This family is characterised by the possession of a fixed actinosoma, which is provided with a sclerodermic corallum in the form of calcareous spicula embedded in the tissues. The spicules are mostly fusiform in shape, and are generally present both in the polypes themselves and in the connecting coenosarc; but there is no central solid axis.
Alcyonium may be taken as the type of the family, and it is well known to fishermen under the name of "Dead-men's fingers." It forms spongy-looking, orange-coloured crusts or lobate masses, which are attached to submarine objects, and are covered with little stellate apertures, through which the delicate polypes can be protruded and retracted at will. The polypes communicate with one another by an anastomosing system of aquiferous tubes, and the corallum is in the form of cruciform, calcareous spicula scattered through its substance. In the allied Sarcodictyon the actinosoma is creeping and linear.
In Xenia the colony is branched, and the polypes are non-retractile ; and in Anthelia and Sympodium the actinosoma has the form of a membranous crust attached to foreign bodies. Lastly, in Sarcophyton (as shown by Moseley) the colony consists of reproductive zooids, which have generative organs and tentacles, and of sexless zooids, which have neither of these organs, but possess a mouth and stomach-sac.