The Littlest, Most Adorable-est Seahorse Fits on Your Fingernail

Because they were a bit gullible, the Ancient Greeks believed a tiny race of humans known as the pygmies did eternal battle with cranes—which, in fairness, can be pretty jerky. Today, “pygmy” lives on in zoology to describe any number of species smaller than their peers, things like pygmy hippos, pygmy goats, and even pygmy killer whales. The most magical among the pygmies, though, is a miniscule creature that’ll punch you right in the face with cuteness, given you can even find it: It’s the charming, fantastically camouflaged pygmy seahorse.

For my money, this is the most confounding camo in the sea. While plenty of ocean critters blend in with their surroundings—the aptly named stonefish, for instance, looks much like a fish, and even more like a stone—and the cuttlefish famously changes its skin color and texture on the fly to match its surroundings, the pygmy seahorse goes about things differently. As a young ‘un, it’ll settle on coral, then adopt one of a number of colors to match and live the rest of its life in that outfit. That’s really, really weird for an animal.

Swimming the reefs of Australia and Southeast Asia are seven species of pygmy seahorse measuring between a half inch and an inch long, small enough to fit on your fingernail. But from here on out when I say “pygmy seahorse” I’m referring to just two, Bargibant’s and Denise’s pygmy seahorses, which stick to coral sea fans known as gorgonians. The other species are great and all, but these two are the most spectacular.

Gorgonians come in a range of colors, and this presents a problem for the seahorses. If, say, they were pink and could only find orange gorgonians instead of pink gorgonians, their camo would be worthless. So when a pygmy seahorse lands on a gorgonian as a black-hued juvenile, it begins an incredible transformation. “It lives on some gorgonians that are kind of warty and branched, and some that are smooth and a little bit darker red, or more pale,” says Steinhart Aquarium biologist Matt Wandell, who was the first to breed pygmy seahorses. “And so it’ll adapt to that color and that texture,” warts and all, over the course of a few days.

Wandell’s seahorses were orange because that’s what color they wanted to be and if you can’t handle that I don’t know what to tell you.

That transformation appears to be permanent, as opposed to the cuttlefish’s on-demand camouflage. To test this, Wandell dropped already-transformed seahorses into tanks with gorgonians of a different color to see if they’d re-adapt, but nothing doing. “It seems like, as far as we know, it’s a one-time switch,” Wandell says. “You can think of it maybe like language in that sense for a child, where it’s a one-time period where it can adapt to a certain type of gorgonian.”

The cuttlefish’s camouflage trick is easy to figure—it’s covered with cells called chromatophores (as are other cephalopods like octopuses and squids), which rapidly expand or contract to flash certain colors. But how the pygmy seahorse is pulling off its color change, scientists haven’t a clue. It does appear, though, that the seahorse is using visual cues as opposed to something like nomming on the gorgonian to assume its color (since the pygmy perfectly imitates the coral’s warts as well).

It’s baffling. From an evolutionary perspective, the development of camouflage is simple: Individuals that look more like their surroundings have a better chance of avoiding predators and surviving to pass down their genes for this effective camo. Over time, a species accumulates these changes into something epic like the satanic leaf-tailed gecko looking exactly like a leaf … and only mildly like Satan. But why would the pygmy seahorse opt to “choose” the appropriate camo for its surroundings when other animals are born with theirs? Mysteries abound.

What is clear, though, is that the camouflage is legit. Divers have reported just a few instances of predation on pygmies, and humans didn’t even find the things until 1969, and it was an accident at that. It was only when a scientist carted a gorgonian back to his dissection table did he notice a pair of pygmies. A no doubt confused pair of pygmies.

“Hey Hon, You Up for Some Role-Playing?”

By this point in your life you’ve probably learned that seahorse sex is backwards, with the male role-playing as a female to give birth to their young. And that’s true to a certain degree. “In pygmy seahorses, the males are the ones that get ‘pregnant,’ and I put pregnant in quotes because it’s not quite like the way we think of pregnancy,” Wandell says.

When a pair comes together, the female transfers her eggs to a pouch on the male’s belly, perhaps whispering now let’s see how YOU like it. He fertilizes them, and the eggs develop inside him and hatch into tiny seahorses, which he pops out one by one, as many as 70 of them (at least in Wandell’s experience with captive seahorses—in the wild it could be different). The kiddos, which sport spikes that will eventually turn into those warty bumps, seem to be attracted to light, and will make their way to the surface to feed on plankton—stuff like fish eggs and creatures so tiny they’re at the mercy of the current—for two or three weeks, dispersing far and wide. Then they’ll head down to a reef, snuggle up with a gorgonian, and begin their transformation.

Here the pygmy waits for food to come to it, or, more specifically, to the gorgonian, which is made up of individual tentacled polyps that snag plankton. “The plankton has hundreds of thousands of different animals in it,” Wandell says. “So we assume there’s this sort of amalgamation of gunk sticking to the polyps, and the seahorses are eating that.”

And indeed, this exploitation may have been what drove to pygmy seahorse to evolve to be so tiny. “One thing we know about evolution in general is that any time there’s a niche where energy can be derived and exploited, something will fill that niche,” Wandell says. “And that coral surface was something that wasn’t exploited by any other animals.”

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