Nudibranchia Content from the guide to life, the universe and everything


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Nudibranchia are amazing. If you happen to be underwater scuba diving they are possibly the most amazing creatures you are likely to encounter.

Nudibranchia are marine gastropod molluscs. They belong to the same family as your garden-variety slug, having no shell at maturity. This is why they are often called sea slugs.

Where to Find Nudibranchia

The word 'nudibranch' literally translates as 'naked gills' because their gills are located on their backs or along the side of their bodies. Nudibranchia inhabit marine environments ranging from the cold waters of the Arctic to the warm waters of the tropics.

Their primary mode of propulsion, like other gastropods, is the single foot extending the entire length of their bodies. Other species like hexabranchus sanguineus (Spanish dancer) use their magnificently coloured mantle to both propel themselves through the water and to startle predators.


Nudibranchia are carnivores. They feed on other soft-bodied sea creatures including soft corals, anemones and sponges. It is from these tasty morsels that they extract toxins and the amazing colours that decorate their bodies. The colours and toxins form part of the nudibranch defence system. The toxins being used as poisons or in stinging cells, and the colours to ward off predators or to blend in with their surroundings.

The nudibranch has a few options when it comes to feeding. Some use their mouth, others use their cerata, which are finger-like protrusions and which are extensions of their digestive systems. The cerata may also contain stinging cells and, in some cases, are used for breathing. A few species harbour green algae inside their bodies to provide them with food. The algae, in turn, obtains its energy from the sun, making this nudibranch species solar-powered.


Nudibranchia are both male and female (simultaneous hermaphrodites), possessing both sperm and eggs. They exchange these with another of the species in a process that may take seconds or a whole day, depending on the species. Both then go their separate ways to lay swarms of eggs, which ultimately hatch to become the amazing creatures known as nudibranchia.

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