2. They look a lot different as babies.
Nudibranchs start life out as larvae and, at this stage, look like a normal snail. They have a shell and have gone through a process called “torsion.”
Imagine going to a Bikram Yoga class, twisting yourself into an impossible position, then going home and having a smoothie without untwisting. This is what torsion is, and it’s the way your average snail prefers to live their life.
But here’s that next fun fact for you: nudibranchs are not your average snail— they’re a type of sea slug! They drop the shell, untwist themselves, and go about their day. It would be like starting your life as a pretzel but untwisting yourself before going to high school.
3. Their colors come from the animals they eat.
No one embodies “you are what you eat” more than the nudibranch. They munch on brightly colored animals like coral, anemones, and sponges. Those pigments give nudibranchs their wild hues.
Here’s another fun fact: nudibranchs are voracious carnivores!
Nudibranchs spend most of their time crawling on the animals they eat. A majority of nudibranchs are only a few inches long, and the biggest barely clears a foot in length. Therefore, camouflaging themselves to match their prey is their go-to strategy. And since they lack a shell, this is a great defense against larger animals who may want a slow-moving snack.
Some species are poisonous and they want potential predators to know it. Like a silica gel packet that says “Do Not Eat,” a nudibranch’s colors can act as a warning.
And (fun fact!) some nudibranch species aren’t poisonous but mimic the colors of their poisonous cousins. This keeps the nudibranch safe from predators without the hassle of being actually poisonous.
4. They reuse other animals’ defense systems.
Fun fact: some species of aeolid nudibranch eat animals with “nematocysts,” or stinging cells. Have you ever been stung by a jellyfish? What you feel are the nematocysts firing off in your skin. While that may ruin your day at the beach, some nudibranchs see that as a Las Vegas-style buffet.
These nudibranchs not only eat animals who have nematocysts— like jellyfish— but reuse the stingers for defense. They move unfired cells up from their digestive track and position them at the ready. That’s the equivalent of eating a harpoon gun for breakfast and it showing up on your back later, ready to fire.
5. Their anatomy is quite different from a human’s.
To put yourself in the shoes of a nudibranch, imagine you have no bones, arms, legs, or neck. Now imagine your lungs are outside your body and located where your legs used to be (fun fact: dorid nudibranchs have their gills circling their booty).
Also, you’re colorblind and only notice changes in dimness. Instead of your teeth sitting in your gums, they’re on your tongue. Your nose is flipped inside out— it looks like two antennas, or in some cases, bunny ears.