Hydroids

Hydroids look like small ferns or feathers growing out of the rock, and almost every diver assumes they are seaweed. They are animals: colonies of tiny polyps sharing a branching stem, each polyp catching plankton with a ring of stinging tentacles. Three kinds turn up constantly around Malta. Aglaophenia species, the classic sea firs, are stiff feather plumes 5 to 20 cm tall in grey, khaki or dull brown, growing in tufts on rock, on wreck plating and on the stems of larger algae. Eudendrium species, especially Eudendrium racemosum, make looser, bushier colonies of pinkish-orange stems with pale polyp heads at the tips. Pennaria disticha adds fine whitish plumes on harbour structures and lines.

They settle wherever water moves: the current-swept corners of Ċirkewwa and Comino, the railings, masts and ropes of the scuttled wrecks, mooring chains, and the shaded lips of reef ledges from the surface down past 50 m. Colonies come and go with the seasons and can appear on a new surface within months.

Stop at one and there is usually a second story running. Aeolid nudibranchs graze them hard - Cratena peregrina, blue-bodied with orange head tentacles, is the common Maltese one on Eudendrium - and sea spiders, skeleton shrimps and tiny brittle stars use the branches as cover.