Disc corals have gotten incredibly popular over the last few years for their ability to have extremely brilliant colors, a single polyp & corallite which is hard to propogate, and because they are just that cool! However disc and tongue corals are not the only free-living corals on certain parts of the reef environment.
Other super neat free-living corals also include Acanthophyllia, Cynarina, Trachyphyllia, and the “walking dendros” or knuckle corals of the Heteropsammia and Heterocyathus genera. Some free-living species are specially adapted to a mode of underwater locomotion by differentially inflating their tissue into billowy, buoyant polyps – allowing the currents and waves to help them get in a general direction.
Other species such as the two “Heteros” have special adaptation that forces their free swimming larvae to settle out onto a sipunculid worm, better known as peanut worms. The Heterocyathus and Heteropsammia corals then grow around the worm but leaving one little hole on the underside for the worm to access the outside world, and when it does, it often can carry its host coral a considerable distance on a daily basis.
There’s an incredibly great write up by noted coral ecologist Andrew Bruckner, on the free-living coral associations and their observations at one particular Great Barrier Reef Habitat. Aquarium observations are neat and all, but there’s no substitute for seeing how corals really interact with their natural environment, waves, sediments, competition and all. The GBR Free Living coral article is a great read and it pairs up well with a similar feature from the Blenny Watcher blog from a couple years back.