Everything You Need to Know About Nudibranch

Snails and slugs are dark, slimy and disgusting…Right? Well…most are, but not the Nudibranch, the most colourful of all the molluscs. One look at them and you just might find yourself falling in love with a sea slug.


Molluscs have always received negative attention for being wet, slimy and smelly. But, if you look beyond their pale and slippery exterior, you’ll find them to be fascinating creatures.

One such mollusc that has captured the world’s attention is the colourful Nudibranch. The size of a teacup, they are invertebrate gastropod molluscs, belonging to the same family as that of snails and forest slugs.

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Called ‘Clown’, ‘Dancer’, ‘Dragon’ and a host of other names, each befitting their unique personalities, Nudibranch give the ocean a vibrant makeover with their very presence.

Here are a few fun facts about these spectacular creatures:

  • They’re literally ‘naked gills’

The word ‘Nudibranch’ is an amalgamation of two Latin words – nudus, meaning ‘naked’ and brankhia, meaning ‘gills’.

Nudibranch have exposed protrusions coming out of their backs. These extensions are the gills which they use to breathe. The gills resemble flower petals and come in a variety of shapes and sizes. There are over 3000 species of Nudibranch on the ocean floor today.



  • They are clownishly colourful

If you’ve seen a Nudibranch on television, you’ll know what I’m talking about. From pine green to fiery orange, Nudibranch come in hundreds of colours. Each colour combination is unique and creates a visual treat on the ocean floor.

Nudibranch derive their colouring from the food they eat. These sea slugs are carnivorous and prey on algae, corals, anemones, sponges and even other Nudibranch. They use two highly specialized and sensitive tentacles called rhinophores on their head to detect the movement of their prey.

Great examples are the Rostanga bifurcata and the Rostanga arbutus, which take the red pigment from the sponges they prey on and transfer it not only on to their skin, but also to the shells of their eggs.

  • They get their toxins from other animals

Nudibranch are masters at toxin accumulation. In addition to stealing their colour, Nudibranch also steal their prey’s toxins. Research by the University of Queensland found that Nudibranch take a variety of chemical compounds from their prey.

Latrunculin A, a type of toxin found commonly in sponges was the most sought-after. This chemical, which causes degenerative neural destruction in animals when injected, was stored in the mantle (the skin) as a defence against predators.

This toxin has a very bitter taste, which discourages predators from coming in for a second bite.

  • They make sounds that even humans can hear

Some types of Nudibranch have been observed making sounds to attract attention. These sounds, which resemble the sound of a wire tapping the side of a glass jar, are made at even intervals. It was first discovered in the year 1884, by a scientist studying Nudibranch behaviour.

It is still unknown whether these vocalisations are to find prey or to attract mates.


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  • They are hermaphrodites

Like all molluscs, even Nudibranch are hermaphrodites, meaning they have both male and female sexual organs.

The mating ritual of Nudibranch is quite unique. Although they possess the reproductive organs of both sexes, sea slugs cannot self-fertilize. They need help from other sea slugs to get the reproductory process started.

In some cases, the Nudibranch may choose to be either a male or female, leaving the other role to be fulfilled by its mate. If both Nudibranch wish to be males, a battle takes place where the first to penetrate the other gets to remain a male; and the other a female.

In some cases, the Nudibranch engage in simultaneous reciprocal mating, where they both take turns to give sperm to the other.

  • They create a mesh net to hold their eggs

When Nudibranch lay their eggs, they create a mesh-like mass on which to deposit them. This mass is made from their bodily secretions during mating. This mass has a jelly-like texture and clumps together. The shape of the mass resembles that of flower petals.

Sometimes, Nudibranch also lay eggs on plants on the sea floor and create a mesh out of these plants by gluing them together with their bodily secretions.

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(Image: Egg mass created by Nudibranch)
  • They develop symbiotic relationships

Most sea slugs spend their time crawling across the ocean floor in search of food. This leads to the growth of dangerous bacteria and algae on their skin. To get rid of these infection-causing bacteria, Nudibranch develop a working relationship with shrimps.

The shrimp lives in the gill folds of the Nudibranch, feasting on the bacteria and algae. This way, the shrimp is well-fed and the Nudibranch remains clean.


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When it comes to molluscs, Nudibranch are some of the most complex species. They give a wonderful insight into invertebrate evolution. One can’t imagine the ocean floor without them.




Written by Nisha Prakash

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