Dead mans fingers (Alcyonium digitatum) are colony building soft corals that are classified asOctocorallia, a group which also includes sea pens and sea fans. This group of corals is characterized by the eight tentacles clustered around the mouth of each polyp in the colony.
The tentacles sit in a circle around the edge and have small branches. Corals in the family Alcyonaria have a horny or leather-like skeleton supported by calcareous pins.
Colonies consist of small coral polyps and are white or orange in colour, but may appear reddish or brownish during periods of inactivity when the individual polyps are withdrawn into the colony. They can be found attached to a variety of substrates, including rocks, shells and stones, where currents are moderately strong to strong. They are occasionally found on the lower shore, but are more common from just below tide level (sublittoral) down to 50metres and sometimes to 100metres. The feathery white polyps appear when feeding.
Mature colonies form thick, irregularly shaped fleshy masses, typically of stout, finger-like lobes that usually exceed 20 mm in diameter. Young, developing colonies form encrustations of 5 -10mm thick. The breadth of colonies are up to 200 mm.
Dead mans fingers is often a predominant member of large scale fouling accumulations on offshore structures, where its presence increases drag and can cause corrosion.