The 100-Foot Sea Critter That Deploys a Net of Death

One of the Monterey Bay Aquarium Research Institute's ROVs photographed this siphonophore at a depth of 3,770 feet, shattering its sense of privacy.

As far as conjoined twins go, they don’t come more famous than Chang and Eng Bunker, who in the 1800s traveled the world lecturing and generally being gawked at by rubes. They even gave us the term Siamese twins (they were from Siam, which is now Thailand). Eventually they settled down on a farm in North Carolina, married two sisters (uh…), and between them sired 21 children.

The logistics of that seem, well, a bit complicated, if not entirely awkward. There are conjoined twins in our oceans, though, that pull off something far more remarkable. These are the siphonophores, some 180 known species of gelatinous strings that can grow to 100 feet long, making them some of the longest critters on the planet. But instead of growing as a single body like virtually every other animal, siphonophores clone themselves thousands of times over into half a dozen different types of specialized cloned bodies, all strung together to work as a team—a very deadly team at that.

“In a way these specialized bodies function as organs,” said marine biologist Stefan Siebert of Brown University, who studies these glorious creatures with the help of remotely operated vehicles from the Monterey Bay Aquarium Research Institute. “Some move the colony, some feed for the colony, some take care of reproduction.” Whereas creatures like you and me have over millennia evolved different parts of our bodies to work as organs, siphonophores have evolved individual bodies themselves into organs. It’s a bit like your liver up and declaring independence from the rest of you, even though it can’t go anywhere.

“Like any other animal,” said Siebert, “siphonophores start off with a single fertilized egg. And this egg develops into a small larva, and at some point this larva will develop its first tentacle, and it has a mouth opening by then.” A stem develops and elongates, and buds begin shooting off of it to grow into functional bodies.

The red feeding bodies of Apolemia lanosa and a bunch of other white stuff that you probably shouldn’t touch unless you were looking to get stung.

Hunting is left to the bodies that dangle tentacles with powerful neurotoxins, snagging small shrimp and such that are unfortunate enough to wander into its curtain of death (or fortunate, really, if they were going for an epic way to die). The prey is enveloped by the feeding body, digested, and dispersed to the rest of the colony by way of the stem. This nutrition is particularly important for the energy-hungry jet propulsion bodies at the front of the critter, which suck water in and squirt it out again to get the siphonophore moving.

Then there are the reproductive bodies, which produce and release sperm and eggs. And the bodies that cover all the other bodies like protective scales, which “can be very rigid, very sturdy,” said Siebert. “Some of the species we see, it’s almost like a tank. It provides a very, very robust shelter.” In addition to dangling stinging tentacles, some varieties of siphonophore are totally covered with stinging cells to protect them from predators, chiefly the majestic ocean sunfish as well as leatherback turtles, which have fairly disturbing spikes in their mouths to keep their gelatinous prey from escaping.

A shot of Apolemia lanosa showing buds that will eventually form into individual bodies.

Now, there is of course the question of exactly how the individual bodies communicate, for instance how the propulsive bodies work together to not only sense their environment, but move en masse—what with not having a brain and all. This is, Siebert says, “an enigma.”

Even though the group that siphonophores belong to, Cnidaria (which also includes true jellyfish), evolved 500 million years ago, their nervous system remains very simple. Siphonophores “have along the stem one long axon, which probably propagates signals from one end of the colony to the other,” Siebert said. “But how they coordinate all this and how the whole colony appears to act as an animal, it’s really not well understood.” It may be a simple way of doing things, but they sure as hell have been doing something right over those half billion years, diversifying all manner of behaviors and physiologies to become one of the oceans’ most prolific organisms.

The glowing lures of this siphonophore mimic a deep-sea copepod, shown in the inset.

One species discovered in 2005 has evolved a particularly sneaky way of luring prey—with actual lures. Among its tentacles are specialized bioluminescent structures, which the siphonophore flicks back and forth. While nearly all deep-sea critters bioluminesce in some way to either communicate with each other or attract prey, the vast majority glow in blue or green, colors that transmit farthest in water. But this species of siphonophore is the first marine invertebrate found to glow red, according to the scientists who discovered it. But why would it put on a red light, other than for the “Roxanne” jokes? Well, its lures look a whole lot like a particular kind of red copepod, a favorite meal for many creatures in the deep. Attack this faux copepod, though, and it’ll be the last thing you do. Indeed, the scientists who first described this species found both the lures and the fish that attacked them in the digestive system of one specimen.

A Portuguese man o’ war, the angry balloon of the sea.

You’re probably better acquainted, though, with a much more dangerous species of siphonophore: the Portuguese man o’ war (technically, they are not true jellyfish, but I’m not about to be the one to break it to them). Far from the elongated body plan of its comrades, the man o’ war has taken the gaseous sack that normally gives young siphonophores a bit of buoyancy and turned it into a massive balloon that floats along the surface.

Unfortunately even for diligent humans doing their damnedest to avoid the man o’ war, its stinger-packed tentacles can become detached in rough seas. “And then they will drift for a while, and all the stinger cells are still active” on the tentacles, said Siebert. “So you can get stung badly even if you don’t see any jellyfish around.” The pain will be excruciating, though stings are rarely deadly. (I’ve said it before but it bears repeating: Do not pee on such stings. It doesn’t help at all, and you’ll only end up smelling funny.)

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