Meet nudibranch the most beautiful snails in the world.

Picture of nudibranch snail.

What do you think of when someone mentions the word “snail” or “slug”?

Most of us think of some slimy, slippery animal that isn’t the least bit pretty, fascinating, or appealing.

Beneath the surface of the sea, however, lives a type of sea slug, a snail like animal, that is so beautiful and colorful that it has been called the butterfly of the seas.

Although most of these creatures are shell-less, they are in the mollusk family, which includes seashells.

What is it? It’s a nudibranch (pronounced nōōdē-brank).


Image of a colorful nudibranch.

The nudibranch was given its name because it is a mollusk without a shell and, therefore, its gills are exposed. Its name means, literally, “naked gills.”

Marine biologists are still learning about nudibranchs, but over 3,000 species have been found and most of them identified.

They range in length from 1/8 inch [0.3 cm] to more than 12 inches [30 cm] and are among the most vividly colored animals in the sea, possessing vibrant orange, blue, purple, yellow, and red pigments.

Even the masses of eggs of some of these animals are beautiful in color and design.

Their eggs are laid in ribbons arranged in various shapes, which have an appearance much like the ribbon you might use to decorate a gift.

These “ribbons” are laid on edge and are formed into a large egg mass resembling a beautiful flower.

Image of nudibranch eggs.

What keeps such a delicate-looking morsel from being nibbled on and eaten by fish and other predators?

The egg case contains a substance that makes them very distasteful to predators, thereby protecting the eggs until they develop into planktonic larvae.

Adult nudibranchs not only are delicate and highly visible but are slow-moving and soft, a seeming paradox in the often severe, harsh, and hostile environment of the ocean—so much so that one marine biologist said, “They amaze and astound simply because they are.”

Yes, it is amazing that they can continue to exist in their environment—particularly that such an appetizing-to-look-at morsel keeps from being eaten by the fish that are attracted by its bright colors and often fluttering appearance.

Many of the soft-bodied nudibranchs are uniquely designed to graze on sea anemones and their relatives the hydroids.

These organisms upon which they feed have stinging cells in their tentacles to stun their prey and to act as a protection against most predators.

The nudibranch, however, is immune to their sting, and when one of these sea slugs eats the stinging structures responsible for the venomous sting of the anemone or hydroid, its remarkably designed digestive system passes some of these poisonous organisms on to other parts of its body to become a defense against marauders who might like to make a meal of Mr. Nudibranch.

Other nudibranchs protect themselves by secreting mucus that smells unpleasant to man and perhaps makes them unappetizing to fish and other predators.

One species, the sea lemon, has a specialized gland that emits a slimy, sour secretion containing sulfuric acid as a defense against predators.

Fish have been observed to grab a nudibranch, only to spit it out in “disgust.”

Observation of this behavior has led scientists to conclude that the association of bright color and repugnant taste and/or a stung mouth produces a learned response that makes the brightly colored sea slug an invitation to an unpalatable meal.

A powerful defense mechanism indeed!

Some nudibranchs enjoy still another defense mechanism; they can swim and are thus able to get away from possible danger of an obstinate foe.

Others are able to cast off parts of their bodies when under attack and get away. Later, these parts are regenerated.

When observing the delicate beauty of the nudibranch in its ocean environment and learning a little about its means of continued existence,