Nudibranchs: Beautiful creatures who lurk deep in the ocean

The blobfish was this week voted the world’s ugliest creature, but in defence of the oceans, they also possess perhaps the most beautiful in the form of nudibranchs.

Even the most critical of eyes is transfixed by these jelly-like creatures, which are often more like the creation of a confectioner high on sugar than the same Mother Nature that concocted the blobfish.

Boasting the most dramatic colours, nudibranchs are members of the slug family and number more than 3,000 known species, with some scientists estimating there may be double this figure. Their name is pronounced new-dee-bronk and is derived from the Latin word nudus (naked) and Greek brankhia (gills). They can grow to up to 31 centimetres and weigh up to 1.5kg and, aside from these super models’ flamboyant OTT cosmetics, they are fascinating in the extreme.

For example, all nudibranchs are hermaphroditic, displaying both male and female sex organs, but chromodoris reticulata goes one better in that it possesses a disposable penis. After sex, it grows another within 24 hours.

Some nudibranchs are solar-powered, storing algae and living off the sugars produced by their guest’s photosynthesis.

But their beauty masks a dark side: They are in fact carnivores, eating sponges, coral, anemones, barnacles, and they will even devour other nudibranchs. They identify prey with two tentacles on top of their heads, and use their audacious colours to warn predators they are unpalatable or poisonous. These poisons often come from their prey — Glaucus atlanticus, for example, will eat a Portuguese Man of War — with nudibranchs passing the stinging cells they’ve consumed to specific parts of their body for use as a defence.

As much as people are repulsed by the blobfish, the opposite goes for nudibranchs and there is even an app for collectors to identify species.

Nudibranchs can also be found in the Irish and British waters.

*For more information see A Field Guide to the Nudibranchs of the British Isles by Bernard E Picton and Christine C. Morrow’s at seaslug.org.uk/nudibranchs California Academy of Science video: youtu.be/cJE-LPcwtP8