What Do You Know About Nudibranchs?

Both a beautifull and colourfull sight underwater, fascinating to both divers and scientists alike, around the world.


All Nudibranchs are animals, which fall under the class Gastropods, which in turn, falls collectively under the umbrella term of mollusks. The class ‘Gastropod’ includes limpets, sea hare, snails and slugs, some with a shell and some without.

Nudibranchs, in their larval stage have shells and a foot. They undergo a transformation as juveniles where their body twists 180 degrees turning them onto their foot, resulting in the gills and anus being carried above the head. In adulthood Nudibranchs are asymmetrical creatures in their form and shape.

These Gastropods come in many different colours, size and forms, over 3,000 species have been identified, but new ones are still being discovered. Their colours range from almost transparent through to flamboyant, bright colours. Some have stripes and spots, others have colourfull appendages on their backs and heads. You can find them in all the world’s oceans, warm or cold water and, sometimes even in tide pools, which are created after the tide has gone out.

Nudibranch (pronounced nooda-brank) derives from the Latin word nudus-naked and the Greek word brankhia- meaning gills. The gills we can see often protruding out of the backs of many of the different species. Tentacles on the head help to taste, smell and be mobile. One pair of these tentacles called Rhinophores have scent receptors, this allows the Nudibranch to find food or companions. To safe guard these vital parts, the Nudibranch can withdraw the Rhinophores into a pocket located under the skin.

There are two Primary types of nudibranch: Dorid and Eolid. The type Dorid breathes through gills found on their rumps, the Eolid have cerata or finger like appendages that cover their backs. The cerata function is to breathe, digest and can be used for defense.

Nudibranch have poor vision, seeing only light and dark colouration. To sense their surroundings and location, this job is done through their Rhinphores and oral tentacles. They move on a broad muscle which is termed ‘a foot’. This flat muscle leaves behind a slimy trail as the Nudibranch moves around on the seabed, some species can swim, albeit only short distances.


The Eolid nudibranch eats prey which may contain nematocysts, they are then stored in the nudibranchs cerata, where they can be used to sting prey. Dorid nudibranchs develop their own toxins or absorb it through their food. These toxins can be released into the water when required, as a means to capture food. Normally nudibranchs are harmless to the human being, with one exception, that is the Glaucus atlanticus. This species eats the Portuguese man- o-war and stores its venom for its own use, which may sting humans.

Nudibranch are carnivorous, they eat sponges, hydroids, barnacles, coral, anemones, fish eggs and sea slugs. Some species are picky eaters and may only eat one type of prey. Their colour comes from the food they consume, and it is used as a warning signal or camouflage. Certain Nudibranch’s will eat coral with algae, here the algae’s chloroplasts are absorbed into the Nudibranchs cerata, here they use the sunlight for photosynthesis to sustain nutrients, which lasts for months.

Nudibranchs are hermaphrodites, they possess reproductive organs of both sexes. They mate with one adult, regardless if it’s male or female. This is important to them, as they move slowly and their breeding ground becomes small when looking for a partner. The eggs are spiral formed, or coiled shape and are deposited directly as larvae into the ocean, they then settle to the bottom.

The life-span of a Nudibranch is very short. It varies from just a few weeks up to the region of one year.

So, on that note, enjoy them when you encounter these enchanting creatures.