Diving Riau Islands – Nudibranchs

The bottom-dwelling, jelly-bodied nudibranch (NEW-dih-bronk) might seem an unlikely canvas for Mother Nature to express her wildest indulgences of color and form. But these shell-less mollusks, part of the sea slug family, bear some of the most fascinating shapes, sumptuous hues, and intricate patterns of any animal

Population

There are more than 2,000 known species of nudibranch, and new ones are being identified almost daily. They are found throughout the world’s oceans, but are most abundant in shallow, tropical waters. Their scientific name, Nudibranchia, means naked gills, and describes the feathery gills and horns that most wear on their backs.

Characteristics

Generally oblong in shape, nudibranchs can be thick or flattened, long or short, ornately colored or drab to match their surroundings. They can grow as small as 0.25 inches or as large as 12 inches long.

Behavior

They are carnivores that slowly ply their range grazing on algae, sponges, anemones, corals, barnacles, and even other nudibranchs. To identify prey, they have two highly sensitive tentacles, called rhinophores, located on top of their heads. Nudibranchs derive their coloring from the food they eat, which helps in camouflage, and some even retain the foul-tasting poisons of their prey and secrete them as a defense against predators.

Nudibranchs are simultaneous hermaphrodites, and can mate with any other mature member of their species. Their lifespan varies widely, with some living less than a month, and others living up to one year.