Absurd Creature of the Week: The Beautiful But Deadly Undersea Raver That Digests Its Victims Alive

UP HERE ON terra firma, we’re treated to all kinds of wildly colorful wildlife: polychromatic parrots, iridescent green beetles, unicorns galloping on rainbows that one time I ate too many pot brownies. But in the depths of our oceans things are decidedly more drab—gaudy colors ain’t going to do you no good nohow in the darkness. You’ll find a creature here, though, that has evolved what is surely the most over-the-top Pink Floyd-esque laser show in the sea: the comb jelly.

These critters, some 150 described species and another 40 or 50 still awaiting names, locomote by beating rows of tiny hairlike structures called cilia. When white light hits them from, say, a submersible’s beam, the cilia break it into its wavelength colors, producing that hypnotic shimmering rainbow. But don’t be fooled by their beauty: Comb jellies—known scientifically as ctenophores (pronounced TEE-no-fores)—are formidable predators with ultra-fast strikes, hoovering up all manner of zooplankton like copepods and other tiny crustaceans and digesting them alive.

Strangely, though, that laser show is probably a happy accident that only really kicks off when we hit them with high-powered electric light, according to Steve Haddock of the Monterey Bay Aquarium Research Institute (MBARI). “In the wild it probably doesn’t happen, or hardly happens at all,” he said. “And I would think it doesn’t actually have an ecological meaning. It’s kind of a side effect of us bringing them up and shining white lights on them.” Even with comb jellies that tend to live closer to the surface, the effect seems negligible until you hit them with artificial light.

A ridiculously beautiful shot of a sea gooseberry and its sticky tentacles. If you were a tiny crustacean, this would be the last thing you saw. Lucky, this photographer was not a tiny crustacean.  S. Haddock, jellywatch.org

Now, comb jellies aren’t true jellyfish, but an entirely different phylum. And unlike jellyfish, they swim mouth-forward, gulping down their victims. They do indeed have tentacles they use to snag prey, but instead of having capsules called nematocysts with harpoon-like stingers, theirs feature cells that produce a sticky secretion. If it sounds like they’re getting evolutionarily short-changed, rest easy knowing many kinds of comb jellies hunt jellyfish, dangling their sticky tentacles to deliberately get entangled with those of their gelatinous foes. It’s essentially a high-five of death.

As soon as the jellyfish hits the tentacles of the centimeter-long comb jelly, it’s yanked in with astonishing speed. “I was watching one under the microscope one time and I totally jumped in my seat because it was so fast,” said Haddock. “I kind of didn’t expect it to happen. It just engulfed it.” Yet for all their speed, they’re incredibly fragile—pick one up and it’ll essentially melt. Accordingly, Haddock’s colleagues at the world-famous Monterey Bay Aquarium keep them in circular “kreisel” tanks that push water down their sides to create a gyre that keeps the comb jellies suspended in the center.

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The bloodybelly comb jelly, so named because it drinks a lot of bloody Mary’s. GIF: Nurie Mohamed/WIRED. Source: Monterey Bay Aquarium

In addition to the jellyfish-hunters, comb jellies come in a wide variety of other body types and ecological niches. One spherical species, known most excellently as the sea gooseberry, dangles long tentacles that snag smaller prey such as copepods. Then there are some that look a bit like biplanes, known as lobates, which cruise along “like crop dusters,” according to Haddock. Instead of dangling their tentacles, theirs are situated along their mouth to snag prey and ferry it inside. Still other species have adapted their cilia into serrated teeth. “They have this whole field that looks almost like a velcro strip or something, with all of these teeth pointed in the same direction,” said Haddock. “And they can actually ratchet themselves over and bite off chunks of other jellies that they’ve captured.”

“I use the analogy of spiders,” he added. “Because spiders can have a sticky web, they can leap out and ambush things, they can make little lasso webs. And ctenophores have similar range of different feeding modes, depending on the species.”

A comb jelly of the genus Deiopea. Note the oral tentacles, which help shovel food into its mouth.  S. Haddock, jellywatch.org

Comb jellies even come in a parasitic variety—well, at least one species that more just kinda resigns itself to parasitism when it literally bites off more than it can chew. This one sets out to engulfsalps, essentially long tubes of jelly that feed on plankton. If some of these comb jellies happen to be too small to wrap themselves around their prey, “they kind of try to bite it and they end up getting their lips just plastered on the side of it,” said Haddock. “And they just sit there with their mouth sucking on it.” (It’s not unlike the curious mating habits of the deep-sea anglerfish, whose tiny male bites onto a giant female, fuses his lips to her skin, and lives the rest of his miserable life releasing sperm whenever she orders it, proving once and for all that romance is in fact quite dead.)

Such a diversity of lifestyles is all the more impressive when you consider comb jellies have a nervous system, but not a brain. Interestingly, earlier this year scientists found the creatures build their neurons unlike any other critter, which they claim could shake up our understanding of the tree of life. The evolutionary history of the comb jelly, though, has long been and continues to be a subject of much debate.

“They have sensors for sensing light and up and down and touch and taste, things like that,” said Haddock. “But the integration is not done by a CPU. It’s basically done by this sort of network of nerves that are connected in a relatively simple pattern.”

With this system, a comb jelly can build what are known as stereotyped behaviors, for instance knowing instinctively to start rotating once prey hits its tentacles in order to bring the quarry up into the mouth. It’s a bit like being on autopilot, only its simplicity is the exact opposite of the complex systems you’d find in jets or the blow-up doll inAirplane.

A comb jelly of the genus Bathocyroe.
 S. Haddock/MBARI

Now, in the deep sea, where perhaps as many as 90 percent of creaturesgive off some sort of bioluminescence, grabbing such prey can attract unwanted attention. Comb jellies themselves bioluminesce blue or blue-green light in brilliant cascading waves, and can even eject sparkling smoke screens when threatened. But if they ingest a flashing copepod, for example, that strobing inside their transparent gut makes them a target.

Quite brilliantly, to deal with this problem many deep-sea varieties of comb jelly have evolved red guts (see photo at right that looks pretty much exactly like the Punisher symbol) or entirely red bodies. Red light has the least amount of energy in the visible spectrum, and therefore doesn’t penetrate as far down in the water column as blue, which has the most energy. A red comb jelly is red because itabsorbs all other colors but red, so it will appear black in the depths, where there’s no red light. It’s a remarkable adaptation for an incredibly fragile creature that would do well to avoid being seen.

So it is that the comb jelly has mastered light, far beyond its accidental laser show for passing submersibles. If you find yourself down there watching them, though, I’d lay off the pot brownies. Things could get … out of hand.

Reference:

Haddock, S. (2007) Comparative feeding behavior of planktonic ctenophores. Integr. Comp. Biol. 47 (6): 847-853

• MATT SIMON