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Nudibranchs and snails

Gastropods are abundant on Indonesian reefs, but they are easily overlooked because most are small, many are nocturnal, and some are very well camouflaged. Nevertheless the diver who develops the habit of carefully scrutinizing the reef surface will soon find many of these delightful creatures.

Nudibranchs. Nudibranchs, the "naked gilled" sea slugs, are the most interesting to the diver. Like common garden slugs, they are snail-like animals that have lost their shells. Nudibranchs are often strikingly colored.

In some species the coloration is clearly cryptic, allowing them to blend in with their chosen prey. Nudibranchs are carnivorous, and most are very prey specific, feeding for example only on particular types of soft coral or sponges. Since these prey animals are often very colorful, so are the nudibranchs.

In other species, it seems certain that coloration serves as a warning to would-be predators that the animals are foul-tasting or poisonous. Nudibranchs are known to produce some very concentrated toxins. Some even have nematocysts, which they obtain from their cnidarian prey and concentrate in the outer layers of their own skin.