The word „nudibranch“ comes from the latin nudus, naked, and the greek brankhia, gills, but they are also called sea slugs.
You can see them in the seas allover the world. They live in shallow sea water and also in the depths up to 700m.


Nudibranchs are a soft-bodied, marine molluscs which are disconnected from their shells after a larval stage.They have an extraordinary colours and forms. So far about 2,300 species of nudibranchs are known.

Nudibranchs are animals found crawling over the sea bottom or sediment and sub-surface.
The body of nudibranchs have many different shapes and colours., They lack a mantle cavity. Some species have attached a venomous part on their sides, which discourage the predators. Many also have a simple gut and a mouth. The eyes are simple and able to realise only light and dark.The eyes are set into the body, are about a quarter of a millimetre in diameter. Nudibranchs vary in adult size from 4 to 600 mm. The adult form is without a shell. Some species have direct development and the shell is disattached before the animal emerges from the egg. The nudibranch breathe through a „naked gill“ placed on their backs.

Nudibranchs have tentacles, which are sensitive to touch, taste, and smell. they are the most colourful creatures on earth.

In the course of evolution, nudibranchs have lost their shell and develop an alternative defence mechanisms. Some species evolved an external anatomy with textures and colours that camouflage them in the surrounding to avoid predators. Other nudibranchs have an intensely bright and contrasting colour pattern that makes them especially visible in their surroundings. Some nudibranchs store the stinging cells in the dorsal body part. They use a variety of chemical defences for protection, but this strategy is not necessary lethal is design to be effective.
Some of the nudibranchs contain a sponge chemicals when they are in the presence of that kind of food source, but they can also change defence chemicals when they change the diet. Certain species are able to produce their own chemicals.
Another method of protection is the release of an acid from the skin. Once the nudibranch is touched by another creature, it will release the mucus automatically.

Nudibranchs have a set of reproductive organs for both sexes, but they cannot reproduse themselves. Nudibranchs typically deposit their eggs within a gelatinous spiral.
A nudibranch called pteraeolidia ianthina is solar-powerd, it has adapted horns to contain zooxanthellae which continue to photosynthesise and provide energy.

All known nudibranchs are meat eaters. Some nudibranchs feed on sponges, others on small predators related to jellyfish, others on small invertebrate animals and some eat other sea slugs or their eggs or, on some occasions, are cannibals and prey on members of their own species.

In Alboran sea where Black Frog Divers dive it is very easy to see a nudibranchs. Many different kinds of those spectacular animals living in this waters and we see plenty of them every single dive. If you are a fan of the most colourful animal on the planet and want to take superb pictures of them, book a dive with us and will promise to deliver an opportunity to see and photograph those amazing creatures.