Nudibranchs – All Your Questions Answered!

Nudibranchs – All Your Questions Answered!

Gordon’s Bay is THE place to find nudibranchs!  You will see so many different types in such  large numbers on every dive in Gordon’s Bay.  Not only are they beautiful to see, fun to search for and make fantastic photographic specimens, nudibranchs are really fascinating creatures too!  Find out more here…

What is a Nudibranch?

Nudibranchs are molluscs in the Class Gastropoda (which includes snails, slugs, limpets and sea hares). Nudibranchs have a shell in their larval stage which disappears before they reach the adult form. In their larval stage, nudibranchs undergo a process called torsion, where the entire top of their body twists 180 degrees on their foot. This results in the placement of the gills and anus above the head, and adults that are asymmetrical in form.

Ink-spot Nudibranch

Inkspot Nudibranch

Where does the name Nudibranch come from?

The word nudibranch (pronounced noody-brank) comes from the Latin word nudus (naked) and Greek brankhia (gills) after their feathery, gill-like appendages. They also have a pair of tentacles (called rhinophores) on their heads which enable them to taste and smell.

Types of Nudibranch:

Worldwide, over 3000 different types of nudibranchs have been discovered.  They can roughly be divided into two types:  dorid nudibranchs and eolid nudibranchs.

Dorid nudibranchs breathe through gills situated towards the end of their backs.

Cape Dorid

Eolid nudibranchs have finger-like appendages called cerata that cover their backs.  Cerata come in all shapes, colours, sizes and design. Cerata are responsible for breathing, digestion and defence.

Coral Nudibranch

Coral Nudibranch

Silvertip Nudibranch

Cape Silvertip Nudibranch with Eggs

How do Nudibranchs Move?

Nudibranchs move using their broad, flat muscle called a foot.  They are also able to swim short distances by flexing their foot which they flatten out and move in undulating movements.

How do Nudibranchs See?

Nudibranchs have very poor vision and can only see light and dark. They can’t even see their own beautiful colouration!  Their sense of the world is obtained through their rhinophores on top of their head and their oral tentacles near their mouths.

What do Nudibranchs eat?

Most nudibranchs are carnivorous and eat sponges, corals, anemones, hydroids, barnacles, fish eggs, and even other sea slugs.  They eat using a radula (rows of tiny sandpaper-like teeth used to scrape food).  Some types of nudibranchs eat only one kind of prey, which helps when searching for nudibranchs – you find the food, you will probably find the nudi!

Black Nudibranch

Black Nudibranch

Some nudibranchs produce their own food by eating algae.  The algae’s chloroplasts are absorbed into the cerata, where they photosynthesise using the sun, providing nutrients which sustain the nudibranch for months.

Why are Nudibranchs so colourful?

Nudibranchs get their bright colour from their food.  They use their colour as a form of protection – either to warn their predators that they are poisonous; or as a form of camouflage to help them blend in against the sponges or corals where they live.

Gasflame Nudibranch

Gasflame Nudibranch

How do Nudibranchs protect themselves from prey?

Eolid Nudibranchs are able to use the stinging cells of nematocysts from the food that they eat to protect themselves against predators.  Instead of digesting the nematocyst cells, these are stored in the nudibranch’s cerata where they can be used to sting predators.

Dorid nudibranchs can produce their own toxins which they get from their food such as sponges.  They then release these into the water as a form of defence when needed.

Variable Nudibranch

Variable Nudibranch

Do Nudibranchs produce slime like snails and slugs?

Nudibranchs, like land slugs and snails, emit slime as they move.  They can emit chemicals into their slime to communicate with other nudibranchs, either to inform them of danger from predators; or to tell them where they are so that they can mate.

How do Nudibranchs reproduce?

Nudibranchs are simultaneous hermaphrodites, which means they have both male and female reproductive organs at the same time and can mate with any mature individual of the same species they happen to find. They lay masses of spiral-shaped or coiled eggs which hatch into free-swimming larvae which eventually settle onto the reefs and sea floor.  Egg ribbons are specific to the type of nudibranch and can be used to find and identify nudibranchs whilst diving.

Crowned Nudibranch

Crowned Nudibranch with egg ribbon

Crowned Nudibranchs

Crowned Nudibranchs Mating

How long do Nudibranchs live?

Nudibranchs don’t usually live very long – some can live for about a year but most only live for two to three weeks.

Are Nudibranchs harmful to humans?

Despite the unsavoury or toxic taste they can present to their predators, most nudibranchs are harmless to humans.

So now that you know a little more about nudibranchs, let’s get diving and go and see how many we can find :D

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