Nudibranchs: Some Awesome Facts About the World’s Strangest & Prettiest Slugs

Nudibranchs or “nudis” are small marine creatures that always intrigued me, and soon after I became a scuba diver, they became my favourite marine animal to find on every dive.

Often called the most bizarre marine creatures out there, you can’t help but fall in love with nudis. They come in different textures, shapes and every colour of the rainbow. There are over 3000 identified species in the ocean, which makes finding a new one on your diving adventure similar to a pokemon hunt!

Even though these strange looking creatures are related to snails, as they evolved they decided to ditch their shells - and who blames them? If I had cool and beautiful colours like them, I would also want to show them off!

In this post, I am going to tell you 10 awesome facts about nudibranchs that will blow your mind.



The name nudibranch derives from Latin, “nudus” meaning “naked” and the Greek word “brankhia” meaning “gills”

If you have ever seen a nudibranch, did you notice their gills are not like most marine animals...Instead of having them on the side of their body, these guys have them stuck on their back exposed to the marine environment - hence the name “naked gills”.


FACT #2 -

They come in every colour imaginable

Coming in many colours, the nudibranch is a master of disguise. It is thought these brightly coloured creatures use their colours to hide from predators or even trick them into thinking they are poisonous.

It is eating different coloured corals, sponges, anemones, and even other nudis where they get their unique colours from!



They have some super rare and cool superpowers

They may be small, but these are geared up with some super cool features!

Superpower 1:

Their little horns, called rhinophores, are sensory organs that allow the nudibranch to distinguish chemicals in the surrounding environment. This allows many nudibranchs to sniff out food, detect potential danger, and identify pheromones given off by potential sexual partners.

Superpower 2:

As they munch on algae-covered corals, they produce solar power...WHATTT?!

It is true! Some nudibranchs can absorb chloroplasts found in the algae they eat for photosynthesis, a phenomenon known as kleptoplasty. This allows them to survive and hold onto energy for months.

Superpower 3:

Never be fooled by their they are soft-bodied, nudibranchs have created a pretty impressive self-defence mechanism to protect themselves. Some have evolved to have tough skin, some bumpy and slightly abrasive, and some even can secrete toxic chemicals and stinging cells.

Some nudibranchs have become quite the cook...making their own poisons, however, most that produce toxic elements obtain them from foods they eat.



Both nudibranch parents lay eggs

Nudibranchs are hermaphrodites so they have both genital systems of a male and female. When things get steamy underwater, two sexy nudibranchs will make contact with their genitals to exchange male gametes so they can fertilise their female gametes, both becoming parents. They lay their egg mass in a frilly spiral (embedded in mucus) on a hard substrate.

This sexual act lasts around 10 minutes, and if you look very closely you can see two penises side by side transferring the goods!

Both parents will become pregnant and give birth to little baby nudibranchs. That is one smart move to increase your population!



Nudibranchs can sacrifice part of their body to protect their core

These guys may be small, but they sure are smart! Nudibranchs can sacrifice parts of their body such as their branchial plumage, their rhinophores, and parts of their mantle to save the essential parts of the body.

Studies have found nudibranchs self-decapitating their heads and then regrowing their bodies, a few days for a beating heart, and a few weeks for 80% body regeneration - this blows my mind! The sea slugs behind this wizardry belong to the group called sacoglossans. Their decapitated body can survive days, sometimes even months without the head, however, scientists said they were unable to grow this back.



Some nudibranchs don’t have to eat

Some nudis don’t have to eat as they can store photosynthetic algae inside their bodies! Once they have munched enough (this only takes a few weeks) they have enough energy for them both.

Saying that some go completely the other way and live for the cannibalism life...rearing up like a horse and landing on their victim (usually go for a different species to themselves).

While we are on the food topic...some people from Chile, Russia and Alaska are known to roast or boil nudibranchs for their supper. Apparently, it is like “chewing an eraser” - maybe I will give this delicacy one a miss...



Nudibranchs are communication pros

Just like their land relatives, nudis leave a trail behind them wherever they go. These trails contain chemical signals that can warn other nudibranchs of any nearby dangers or lure a potential sexual partner so they can get their groove on!

These guys are not the best when it comes to telling if it is light or dark underwater, so they also create chemical signals to locate food and other nudis using their oral tentacles (located on either side of the mouth).

Nudibranchs can cover a pretty impressive distance for their size. If they sense a signal far away, they can release their muscular foot that anchors them and swim or tumble to their desired location - so if you ever see a nudibranch floating away from the reef, do not disturb them, there is a reason they are on the move!



At least two species of nudibranchs can make sounds audible to humans!

In 1884, a scientist named Professor Grant reported observations of 2 nudibranch species emitting sounds that humans can hear. He said: “ Eolis punctata [Facelina annulicornis], and Tritonia arborescens [Dendronotus frondosus], certainly produce audible sounds.” This apparently sounded like wire, tapping on a jar, repeated over 1-2 minute intervals.

The reason behind the sound is still unknown, but it is thought to attract mates or for defence.

This would be the perfect PhD research for anyone obsessed with nudibranchs.



Nudibranchs live a very short life

These beautiful and strange-looking marine creatures unfortunately are short-lived, so enjoy them while you can! Most survive only a few weeks, and the lucky ones just over a year.


FACT #10

Nudibranchs are important to science

Scientists are studying nudibranchs to find out if they can be useful for human medicines. They are the prime candidate when it comes to uses in marine pharmacology and biotechnology as they lack physical defence mechanisms and are soft-bodied marine organisms.

24% of marine natural products already come from these teeny tiny creatures, focusing on their involvement in anti-cancer drugs.

Now you can see how awesome these little guys are! On your next dive over a reef take a look and see how many you can find!


Books for Nudibranch Lovers!

With so many nudibranchs out there, if you are a lover like me, I highly recommend buying the following books:

  • Nudibranch & Sea Slug Identification - Indo-Pacific- 2nd Edition by Terrence Gosliner, Angel Valdes & David Behrens

  • Nudibranch Behaviour by David Behrens

  • Nudibranchs of the World by Helmut Debelius


Written by Darby Bonner

PADI OWSI & Marine Biologist

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