The Nudibranch – Most Colourful Ocean Creatures Of The Sea

nudibranches sea slugs most colourful ocean life cretures a

Nudibranchs are a collection of soft-bodied, marine gastropod molluscs which shed their shells after their larval stage.

They are recorded for their often unique colours and striking forms. They have been given colourful nicknames to suit, such as “clown,” “Marigold,” “dancer,” “splendid,” “dragon,” or “sea rabbit.”

Currently, approximately 3,000 valid species of nudibranchs are identified.
The term “nudibranch” originates from the Latin nudus “naked” and the Ancient Greek βράγχια (bránkhia) “gills”.

Nudibranchs are often informally referred to as sea slugs. They are a family of opisthobranchs (sea slugs), inside the phylum Mollusca (molluscs). Still, many sea slugs belong to several taxonomic groups which are not strictly related to nudibranchs.

Many of these other sea slugs, such as the photosynthetic Sacoglossa and the colourful Aglajidae, are frequently confused with nudibranchs.

Nudibranches sea slugs most colourful ocean life cretures

NudiBranch Facts

  • Most Common Name: Nudibranchs
  • Scientific Title: Nudibranchia
  • Marine Type: Invertebrates
  • Diet and Feeding: Carnivore
  • Typical Lifespan in the Wild: Up to 1 years
  • Dimensions: 0.25 to 12 inches
  • Weight: Up to 3.3 pounds

Nudibranch Distribution and Habitat

Nudibranchs live worldwide in seas ranging from the Arctic to temperate and tropical areas to the Southern Ocean in Antarctica. Although a few varieties inhabit water with lower salt content than brackish water, they are almost entirely confined to saltwater.

Nudibranches sea slugs most colourful ocean life cretures

Nudibranchs live at all depths, from the tidal zone (the tidal zone is the region where the ocean meets the landmasses between low tide and high tide) to depths of well over 700 m. The most tremendous diversity of nudibranchs is seen in heated, shallow reefs. However, a new nudibranch species was found at a depth near 2,500 m (8,200 ft).

Nudibranchs are ground dwellers that crawl over the substrate. The only exemptions to this are the neustonic Glaucus nudibranchs, which float upside down just beneath the ocean’s surface; the pelagic nudibranchs Cephalopyge trematoides, which swim in the water column; also Phylliroe bucephalum.

The bottom-dwelling, jelly-bodied nudibranch (NEW-dih-bronk) might seem an unbelievable canvas for Mother Nature to display her wildest indulgences of colour and style.

But these shell-less molluscs, part of the sea slug family, bear some of the most captivating shapes, sumptuous hues, and intricate designs of any ocean animal. The cute and colourful sea animals are one of mother nature’s most awe-inspiring creations.

Nudibranches sea slugs most colourful ocean life cretures

Nudibranch Population

There are higher than 2,000 known species of nudibranch, and new ones are being identified nearly daily. They are located throughout the world’s oceans but are most plentiful in shallow, tropical waters.

Their scientific name, Nudibranchia, means naked gills and represents the feathery gills and horns that most carry on their backs.

Nudibranch Characteristics

Usually oblong in shape, nudibranchs can be thick or flattened, long or short, ornately decorated or drab to match their surroundings. They can grow as tiny as 0.25 inches or as big as 12 inches long.

Nudibranches sea slugs most colourful ocean life cretures

Nudibranch Behaviour

They are carnivores that gradually range and graze on algae, sponges, anemones, barnacles, corals, and even other nudibranchs. To distinguish prey, they have two highly receptive tentacles, called rhinophores, placed on top of their heads.

Nudibranchs obtain their colouring from the food they eat, which helps in camouflage, and some even hold the foul-tasting poisons of their prey and discharge them as a defence against predators.

Nudibranchs are simultaneous hermaphrodites and can mate with any other adult member of their species. Their lifespan varies extensively, with some living for shorter than a month, and others living up to one year.

Nudibranches sea slugs most colourful ocean life cretures

9 Strange Reasons That Make NudiBranches One of the Most Unique & Colourful Sea Creatures On Earth

Nudibranchs, a collection of soft-bodied and wonderfully colourful molluscs, are often confused for sea slugs. But these gastropods couldn’t be more diverse — or more appealing.

What Does Nudibranch Mean?

The “nudi” in nudibranch means naked, and the “branch” indicates gills.
Their scientific name translates correctly as “naked-gills” because their breathing apparatus is usually exposed.

Nudibranches sea slugs most colourful ocean life cretures

Strange Reproductive Systems

They are also all hermaphrodites; they have male and female sexual organs, but they do not inseminate themselves.

Sex usually happens as a mutually advantageous affair with a partner nudibranch.
As a common rule, they mate top to tail — it is called reciprocal neck mating.

And some species have a penis that fastens off in their partner and then renews!

Their backsides are … unusually located.

The nudibranch anus is not at the end of the creature, or the bottom, but can occur in a number of areas across different species.

Oddly, in some, it is right in the centre of the gills on the top of the body.

Nudibranches sea slugs most colourful ocean life cretures

They enslave plants to use for solar power and energy.

Some nudibranchs “farm” symbiotic algal cells, named zooxanthellae.
The little cells have adjusted to living inside the tissue of the nudibranchs, and as they photosynthesise, they give the slug sugars.

They use a chemical defence to shield themselves from predators.

Some nudibranchs are known to own chemical defences — meaning, they taste yucky to predators, and might also be toxic when ingested.

Early scientists often included the flavour of the nudibranch in their description, which they experimented on by licking them. Needless to say, this is not a common custom now and is not advised.

Nudibranches sea slugs most colourful ocean life cretures

Along with the chemical, defence comes very dazzling colours, used as a warning: it is nature’s equivalent of shouting “Stay away! Don’t eat me! I’m toxic.”

Intriguingly, some nudibranchs are brightly coloured but do not have chemical protection. These nudibranchs are copying these warning signs, without the nasty follow-through taste.

Crafty! This is called natural mimicking and can allow these unique sea creatures to pretend they taste awful, but actually aren’t.

Some nudibranchs are able to absorb their prey’s defence methods.

They can eat some small venomous jellyfish, consume their toxic harpoons, and move them to the end of their cerata (the wavy, tentacle-like extensions on their exteriors) to use in their own protection!

Nudibranches sea slugs most colourful ocean life cretures

There are just so many of them.

The often-cited figure has more than 3,000 species of identified nudibranchs in the seas, but there are still many more yet to be classified or even discovered.

It is thought there are 400 species of nudibranch — which, by the way, are in the same taxonomic class as the snails and slugs in your backyard — just in Tropical Northern Australia.

They can also get quite large: one type of these cute sea creatures, the Spanish Dancers (so named because their swimming behaviour makes them look like a flamenco skirt fluttering around) can get up to half a metre long!

Spanish dancer nudibranch
Spanish dancer nudibranch

Their babies are basically egg ribbons.

Nudibranch eggs differ somewhat in appearance between species but are usually coiled or wavy in shape.

Picture a spiral that curls loosely, resembling a cross between a bit of pasta and possibly a rose created out of haberdashery.

It is made of tiny nudibranch embryos hung within a jelly-like substance. The jelly gives nominal protection to the embryos, as there is usually no parental care.

Nudibranchs also go through metamorphosis: from the egg, a larva is hatched that floats about on the tide; then, when the right cues are present, they go into a metamorphosis into their adult body.

Nudibranches sea slugs most colourful ocean life cretures

They navigate using chemical sensors.

Nudibranchs sometimes have eyes — though usually, they are only useful for discerning light from the darkness.

They find their way across the ocean utilising little stalks with thin layers of folded tissue named rhinophores, which are chemically sensitive.

Using these, nudibranchs can sense the compounds given off by their favourite food and make progress towards it.

People also ask

Are nudibranchs dangerous?

Despite the unpleasant or toxic taste they can give to their non-human predators, most nudibranchs are harmless to humans, excluding those like Glaucus atlanticus which eats nematocytes and so may consider you a predator and sting you.

Nudibranches sea slugs most colourful ocean life cretures

Is a nudibranch a sea slug?

Nudibranchs are often called sea slugs, as they are a species of opisthobranchs (sea slugs), in the phylum Mollusca (molluscs), but many sea slugs belong to various taxonomic groups which are not strictly related to nudibranchs.

How big is a nudibranch?

Usually oblong in shape, nudibranchs can be thick or flat, long or short, ornately coloured or dull to match their surroundings. They can grow as small as 6.35mm (0.25 inches) or as large as 30 centimetres (12 inches) long.

What eats a nudibranch?

‘Nudis’ have few predators and are in danger only from other nudibranchs, turtles, some types of crabs and humans. Over years of evolution, they have dropped their protective shell and so rely on different forms of protection and protection to deter would-be predators.

Nudibranches sea slugs most colourful ocean life cretures

Do nudibranchs eat coral?

Montipora Eating Nudibranchs are a variety of aeolid nudibranchs which are recognised to feed on coral.

These nudibranchs can consume large quantities of coral in a very short time. They can cause damage quickly because they reproduce at an astounding rate, and they collect the nematocysts (stingers) of their ingested prey.

What is the difference between a sea slug and a nudibranch?

A nudibranch is essentially a sea slug, but there are some varieties of sea slugs that are not nudibranchs. They fall into two main families, which are dorid nudibranchs & eolid nudibranchs.

The main distinction between these two groups is their appearance and which body components they use to breathe.

Further reading


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