This Crazy-Looking Sea Slug Has an Ingenious Secret Weapon

The blue dragon nudibranch eats the stinging cells of the Portuguese man o' war, then incorporates them into its own skin. That, as biologists say, is pretty baller.

In the movie 8 Mile, an underdog rapper who chose the wrong name, B-Rabbit (played by Eminem), surprises a fella who chose the right name, Papa Doc, in a climactic rap battle. Turns out B-Rabbit knew exactly what disses Papa Doc would hit him with. So he appropriated them into his own lyrics, much to the surprise of Papa, whose real name is sadly Clarence. And B-Rabbit won the battle, to much applause.

That’s real cute, says the nudibranch, but I started pulling those moves ages ago—on deadly sea creatures. All over our world’s oceans, the many astoundingly colored species of nudibranch are eating things like the vicious Portuguese man o’ war, incorporating their stingers or toxins into their own skin, and using them to fend off predators. This is an Eminem slug if there ever was one (Eminem, if you’re reading this I’m sorry please don’t hurt me), only instead of appropriating mean words, it’s stealing wonderfully evolved weapons and using them to its advantage.

Nudibranchs are bizarre mollusks that have made a tradeoff: Lose the blasé shell, which takes gobs of energy and resources to construct, in exchange for a far more sinister defense. Different species have become specialized in sequestering the various defenses of both stinging and toxin-coated critters, “which is great because it saves them a lot of energy from having to create these defense mechanisms on their own,” said biologist Shayle Matsuda of the California Academy of Sciences.

How exactly they’re able to absorb the defenses of other animals is not yet clear. What we do know is that some nibble on sponges, others corals, and still others jellyfish, moving their prey’s defensive stingers or chemicals through their own digestive system, out through the walls of the gut, and into sacs on the skin. Here they lie ready to inflict agony on anything that didn’t get the very clear memo not to attack these things.

Bright colors mean “don’t touch me” and “I’m ready for spring fashion lines.”

That memo, of course, is the nudibranchs’ astonishing color scheme: bright, obnoxious, polychromatic madness. Name a flashy color, and there’s probably a nudibranch that rocks it, like a 1980s neon nightmare. It’s so effective, in fact, that other kinds of harmless creatures like flatworms and juvenile sea cucumbers will actually mimic nudibranchs, “so you’ll see a lot of different animals try to take advantage of the fact that predators are learning that that particular color pattern is not something they want to be ingesting,” said Matsuda.

Perhaps the most spectacular of all nudibranchs is the so-called blue dragon (shown at the top), a gorgeous little species with starburst projections known as cerata. Like all nudibranchs, it tracks down its food not so much with sight, but instead with chemical cues. (And unlike the vast majority of nudibranchs, it actually gets its lazy butt off the seafloor and into the water column. Another species, the Spanish dancer shown in the video below, does the same in a rather more spastic manner.) The blue dragon specializes in attacking the Portuguese man o’ war, which is not technically a jellyfish, but a colonial siphonophore made up of thousands of cloned individuals. The man o’ war floats on the surface thanks to a gas-filled chamber, and the blue dragon approaches it in a most remarkable way.

“What it does is it hangs upside down and uses the water tension to basically crawl along the underside of the surface of the water,” said Matsuda. “And then it eats the tentacles of the Portuguese man o’ war.” Now, this is a famously dangerous creature that it’s attacking, but by appropriating its stinging cells, the blue dragon becomes even more dangerous to the fish that unwisely assault it. “Because the nudibranch is concentrating those stinging cells, to touch one of those can actually be more venomous or painful because there’s so many more cells.”

You’re probably wondering by now how exactly the nudibranchs are able to get away with this scalawag behavior without getting stung or poisoned. Well, they are suffering a bit actually, but they have adaptations to deal with the attack. “Some of them have a mucus that helps to stop that, or internal plates that will help lessen the punch toward them,” said Matsuda. (Interestingly, another totally unrelated creature that eats jellies, the incredible ocean sunfish, uses the same mucus defense.)

Now, such an amazing diversity of nudibranch habits necessarily warrants a range of tools. Nudibranchs don’t have teeth like we or sharks or other fish do. Theirs are more like a conveyor belt, a ribbon of teeth known as a radula. “What they do is when they find something that they want to feed on, which is usually something more flat like a sponge or a coral polyp, they extend the ribbon out of their mouth and will scrape off whatever it is,” said Matsuda. “It feels kind of like a cat tongue or sand paper.”

Some nudibranchs, though, don’t hunt such resilient game. Certain species opt to gobble up algae and end up stealing their chloroplasts, the bits of plant cells where photosynthesis takes place, and store them in their skin. Indeed, these nudibranchs are a lovely bright green, and may in fact be partly solar-powered, though Matsuda notes that there’s still quite a bit of debate on whether the nudibranchs are able to actually draw energy from the chloroplasts.

Nudibranch egg ribbons are the closest you can get to an underwater rose…that’ll explode at some point with thousands of baby sea slugs.

And because why stop at being beautiful as adults, nudibranchs have some of the most gorgeous, colorful eggs in the sea (certain shark species have sweet spiral eggs, but they’re a bit drab). Females lay thousands and thousands of them arranged like wavy tortilla bowls that come in all manner of hues. In fact, it’s these characteristic egg ribbons that help scuba-diving biologists to not only track down nudibranchs, but to identify the species that laid them. And it won’t necessarily be a female that’s likely nearby: Nudibranchs are hermaphroditic, and take turns fertilizing each other (if that’s not also beautiful, I don’t know what is).

Read more at Wired Science