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Animal of the Week: the Nudibranch

By Sara Umbrell, Layout Director


This week’s animal of the week is going to “branch” out into the world of invertebrates and talk about the nudibranch, aka the sea slug! These funky creatures were first discovered in 1894 by a pearl farmer off the coast of Western Australia. He at first mistook it for a floating sheep lung (which was apparently common at the time), but after some more observation he identified it as a nudibranch, which roughly translates to “naked gill.”


The nudibranchs are very vibrant organisms, with some of the most brilliant coloring of the marine animals. Right now, there are about 3,000 identified species of nudibranch, but it’s estimated that this is only half of all existing species. Most nudibranchs are part of two subcategories: dorids or eolids. Dorids are usually smooth and thick, with a broad, flat body and exposed gills on their back. Meanwhile, eolids are typically slim, with their body covered in cerata which can come in the form of spines, ridges or pustules. These cerata have a variety of functions, serving as gills, an extension of the digestive system and a storage space for toxins it absorbs, and they can even detach from the body to act as a decoy for predators.


All species of nudibranch, regardless of where they live, lack a shell. To make up for their lack of shell protection, the nudibranch utilizes multiple tactics to avoid predation. Nudibranchs can eat other species like anemones and jellyfish without being harmed by their stinging defense, nematocysts. Instead, they absorb them and use them for their own defense to shoot at potential predators. Some nudibranchs can also absorb toxins from other animals onto their mantle (their skin), and that toxin then sits like a layer of mucus to ward off anything that might try to take a bite out of it.


All nudibranchs are hermaphrodites, which means that they have no set male or female in the species. During mating, both individuals will receive a fertilized egg after the process is complete. The nudibranch is found almost all over the sea, from the open ocean to the intertidal zone, although a lot of species are found crawling in the benthic zone, or the ocean floor. So the next time you’re at the beach, look out for the reclusive nudibranch!



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