Nudibranchs are marine slugs! They are members of the mollusk phylum and gastropod class. They and are found mostly in shallow tropical waters and there are some 3,000 known species. They are usually quite small (6 mm) and many display an amazing array of colors. Nudibranchs feed on sponges, hydroids, corals, bivalves, and even other nudibranchs! Many nudibranchs are toxic – some members have the unique ability to incorporate defense mechanisms from the prey that they eat: nematocysts (stinging cells) from hydroids and toxins from sponges can become part of the nudibranch’s defense mechanisms. Nematocysts from consumed prey such as hydroids, anemones, and coral are found on the tentacles of the nudibranchs. Many members get their color from the prey that they eat.
Nudibranchs come from the scientific name Nudibranchia. This literally means naked gills. They can be distinguished by rhinophores on the top of their head. Nudibranchs are also hermaphrodites – that is, they can reproduce with both sexes of the species.
If you like looking for small critters, finding a nudibranchs on a dive is a definite treat. But, make sure you have a macro lens on your camera!