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Interesting Facts About Nudibranchs

Rutuja Ghanekar
Displaying a ravishing show of colors, nudibranchs are akin to snails, but they got rid of their shell and evolved into all-muscle animals millions of years ago. Read about their mysterious underwater life.

Did You Know?

With a length of approx. 20 inches,Hexabranchus sanguineus (Spanish dancer) is one of the largest nudibranchs ever recorded.
The word nudibranch comes from Latin (nudus=naked) and Greek (brankhia=gills) origin. Informally referred to as sea slugs, nudibranchs have been traditionally classified as members of the suborder Nudibranchia, belonging to the class Gastropoda.
Not all sea slugs are nudibranchs, since there are several sea slugs belonging to other groups exhibiting characteristics different to those of nudibranchs. The most striking feature these mollusks possess is a vibrant-colored body.
With more than 3,000 known species, nudibranchs have an average lifespan of a mere 1 year in the wild. Here are the other fascinating attributes nudibranchs are endowed with.
  • Chromodoris Leopardus
  • Chromodoris Willani
  • Trinchesia Sibogae
  • Cratena Peregrina
  • Nembrotha cristata
  • Hypselodoris bullocki
  • Phyllidia arabica
  • Triopha Catalinae
  • Halgerda batangas
  • Mexichromis multituberculata

Distribution and Habitat

Nudibranchs are bottom-dwelling mollusks found on the sea floor of oceans worldwide. They are usually found below the intertidal zone, but can also be found in depths of more than 700 m. They also live in tidal pools, coral reefs, rocky, and muddy areas—right from the tropics to Antarctica, but largely inhabiting tropical waters.
While most nudibranchs are benthic, gliding using their muscular feet over bottom substrates, there are certain varieties, like Cephalopyge trematoides, that inhabit pelagic waters.

Physical Features

The size of nudibranchs can vary between 0.25 inches to 12 inches, and they weigh up to 3.3 lbs. They are soft-bodied animals having elongated muscular foot tentacles for locomotion. They usually crawl or drag themselves using their feet, where the tentacles cling on to sponges, corals, and rocks.
Scientists are of the opinion that since these invertebrates have limited sight owing to their rather small and weak eyes, the rhinophores (tentacles) present on their head are helpful in sensing and gaging the nearby environment. Oral tentacles are also used for the function of smell, taste, and sense of touch.
For the purpose of respiration, some nudibranchs possess structures similar to tentacles, known as cerata, all over their body, while others have a bunch of gills on the back of their body.

Diet and Reproduction

Being carnivorous, nudibranchs feed on sponges, anemones, tunicates, corals, algae, and, even other smaller nudibranchs. The rhinophores on their head help them locate and identify their prey before attacking it. They consume food with the help of a strong, toothed structure inside their mouth called radula, that aids them in breaking down the prey.
Nudibranchs are hermaphroditic—that is, having both male and female reproductive organs. But they often do not self-fertilize, and given their solitary lifestyle, can only do so when they encounter a nudibranch belonging to the same species.
Eggs are laid in millions, generally on the surface they are feeding upon. They are laid either in the form of ribbons, coils, or in tangled masses.

Defense Against Predators

Over the years, nudibranchs have evolved into shell-less invertebrates to self-guard themselves against ferocious predators. While some have developed to sync with the surroundings using camouflage as a defense technique, others have evolved into bright hues of colors and textures that are obvious to the eye.
The vibrant display of color is imbibed in order to ward off predators by making them think that nudibranchs are poisonous and disgusting. However, not all nudibranchs create their own poison. Some extract poisonous chemicals from their prey such as toxic sponges.
Here, when nudibranchs feed on poisonous sponges, they store the chemicals in their body, and release them when threatened. Nudibranchs, feeding on hydrozoids, corals, and anemones, have the ability to store their stinging cells, called nematocysts, without causing any harm to their own body, and use them when disturbed.
Scientists today are trying to isolate the chemicals these animals store, and study whether the same can be helpful to humans. Since nudibranchs are harmless to humans, they are often devoured by roasting or boiling them, or even eating them raw!