False coral

False coral is the small orange-red shrub you keep finding on the shaded roof of an overhang and keep assuming is coral. It is a bryozoan: a rigid colony of thousands of microscopic box-shaped animals, each in its own chalky compartment, that between them build a branching skeleton. The branches are stubby and cylindrical, three to six millimetres thick, forking repeatedly, and the giveaway is the tips: they are flat and blunt, as if the whole colony had been trimmed with secateurs, which is where truncata comes from. Colour runs from orange through coral-red to a dull brick, fading to chalky white when the colony dies. A typical Maltese colony is a tuft five to ten centimetres across; a big old one reaches fifteen.

It wants shade and hard rock, so look on the ceilings of overhangs, in the twilight zone just inside cave mouths, on shaded vertical faces and on old wreck plating. It grows from a couple of metres down to over a hundred, but in Malta and Gozo you will see it best between about five and forty metres, at sites like the Blue Hole, Billinghurst, the Inland Sea tunnel and the underside of the Ċirkewwa arch, usually mixed in with scarlet sponge crusts and small gorgonians.

Up close, and only with a torch, the surface is finely pitted: each pit is the doorway of one animal, which pushes out a tiny ring of tentacles to filter the water. Because its branch thickness responds to how much abuse and sediment it endures, researchers have used it as a measuring stick for how heavily a coralligenous reef is being dived.