False black coral

Also called the gold coral, this is a zoanthid living a very odd life. It starts as polyps settling on a living gorgonian, kills the host tissue back branch by branch, then coats the bare skeleton and thickens it with a hard, dark, horn-like material of its own. What you end up with is a stiff, tree-like colony, dark brown to near black at the core, covered in fat golden-yellow polyps each ringed with short tentacles. Colonies commonly reach half a metre and the big ones are well over a metre across.

In the Mediterranean it is a rare, patchy species of dim circalittoral rock, typically from about 30 m down to a couple of hundred metres, and it has been recorded from Maltese waters. Realistically it is a deep-wall and technical-depth find here rather than something on a standard recreational profile: think the shaded faces below 40 m on the offshore pinnacles and drop-offs.

It is also one of the longest-lived animals in the sea. Growth-band work on Mediterranean colonies has put ages in the thousands of years, which makes any encounter with a large specimen a genuinely unusual moment and any damage to one effectively permanent.