What do you know about nudibranchs? If your answer doesn’t include at least 5 fascinating facts, then it’s time to read this article! Nudibranchs are marine gastropod mollusks (sea slugs) that comprise over 3,000 different species. They live all over the world in tropical and subtropical waters. Their beautiful coloration, friendly demeanor, and interesting feeding habits make them popular among scuba divers and marine biologists alike. Below are five fascinating facts about nudibranchs that you probably never knew!

Where do nudibranchs live?

These sea slugs live in all of Earth’s oceans, from Arctic waters to Antarctic seas. They can also be found on rocky shores and mangrove swamps, as well as in tide pools. Most nudibranchs are marine creatures; however, some live in salt marshes and even brackish estuaries. When it comes to terrestrial environments, a handful of species can survive on land for several hours or days—but they always return to their home waters at nightfall.

How can they have so many colors?

Have you ever seen a creature with more colors than a cuttlefish? Their skin features an entire rainbow of hues, ranging from electric blues to vibrant reds and deep purples. But how do they have so many colors? It all comes down to their pigmentation, which is controlled by tiny light-reflecting plates called iridophores. This may not be as complex as your favorite gemstone, but it’s certainly far better than whatever color you dye your hair!

Why do they taste bad?

Certain types of nudibranchs taste bad to predators. While some species, like Aeolidia papillosa and Hypselodoris bullocki, can produce mild toxins that act as a deterrent, most are covered in stinging cells called cnidocytes. These structures contain a neurotoxin that causes a chemical reaction resulting in numbness or irritation on contact with human skin. In some cases, their defenses are so potent they’re considered dangerous to touch.

What makes them toxic?

While most nudibranchs are bright and colorful, some species contain a toxic substance that can cause human irritation. In extreme cases, these creatures have been known to kill dogs. Thankfully, not all nudibranchs contain toxins—but if you’re planning on scuba diving in an area where they live, it’s best to be aware of which species are toxic and which aren’t.

Are nudibranches endangered?

The abundance of these brightly colored, shell-less sea slugs is actually going down. Researchers believe climate change and ocean acidification are to blame for nudibranches’ decreasing population. They’re also at risk of being hunted for their venomous toxins, which may be a new source of medicine or other products. Hopefully, these amazing creatures won’t disappear from our oceans any time soon!

All of the images featured in this article were captured in Fiji.

Bonus image – Trinchesia sibogae