Bushy mass of seemingly disorderly branching colonies, that first appears as a light grey mass to the approching diver when the white-translucent polyp tentacles are fully deployed. Unlike Feather Black Coral (q.v.) secondary branchlets grow off their main branches in no particular order. Rather than black, branches are lighter in colour, ranging from orange to dark brown.

Unlike other corals, stony in particular, Black Corals do not form polyp coralites as such, with polyps each developing a system of radial tentacles. These do contract when needed, but cannot completely retract within the branch structure.

NOTE: Black Corals owe their name to the fact that their branches exsude a dark coloured protein, which builds up in successive concentric layers.