Scientists call them the "unicorns of the sea". The saltiest divers may go a lifetime without ever spotting one. And even decades after their discovery, the elusive creatures remain blanketed in mystery.
Yet every once in a while, a pyrosome shows itself to the world.
This strange, red windsock was spotted off the coast of Akumal, Mexico. It is very much alive, and made up of thousands and thousands of tiny clones.
The crew of Expedition Akumal came across the colony while working to remove invasive lionfish from the local reefs. With over 20,000 dives logged between them, not a single member of the team had ever seen a pyrosome. In fact, they initially mistook the Borg-like creature for trash.
"It was drifting and hovering in an odd way at about 80ft of depth," recalls diver Ivan Perez. "We remove any plastic we find so that turtles will not mistake it for jellyfish and try to eat it."
As the team approached the drifting structure, its true nature was revealed: the tube was not man-made, but rather a colony of tiny organisms called zooids.
"As we watched, it became more mesmerising!" says Perez. "It was open at one end with nothing inside and yet it seemed to move as if the tapered end was some kind of head. There were no eyes or anything like a face. It was entirely made up of tiny, clear elongated bubbles. Each had a spot of red in it. These tiny creatures made up a whole."
The zooids that make up one long pyrosome are clones of one another, with each individual capable of adding to the colony by copying itself. They manoeuvre around using a suck-and-blow strategy akin to jet propulsion, working together as one singular organism to pull and push water through tiny slits in their bodies.
"And like members of the Borg, which are mentally connected, pyrosome members are physically connected– actually sharing tissues," adds marine bioligst Dr Rebecca Helm.
A pyrosome's shape is held by a gelatinous "mucus baloon", which suspends each zooid within its walls. The individual mouthparts are aimed away from the balloon's hollow interior, continuously taking in water as they move fluidly through the ocean. Nutrients are filtered out, and any waste is passed on into the empty space in the middle, where it flows out into the sea.
And as we all know, many hands make light work. A zooid may be just a millimetre long, but reports exist of animals as large as penguins getting trapped within the tube's interior. They might be feathery and delicate as individuals, but a pyrosome colony produces a relatively strong current.
The colonies are often confused with squid egg masses because they're similar in appearance – in fact, we actually made that mistake ourselves when this one popped up on YouTube:
It's an easy mix-up, but Smithsonian Museum of Natural History squid expert Dr Michael Vecchione confirms the Akumal sighting is definitely a large pyrosome.
The specimen is impressive, but these animals can get much, much bigger. Pyrosomes are known to reach lengths of 60 feet (18.2 metres) in length – that's longer than most whales!
Though they're rarely seen by divers, these animals aren't exactly inconspicuous, so what's to stop marine predators from feasting on the largely defenceless colony? The clue is in the name, which comes from the Greek "pyro" (meaning "fire") and "soma" (meaning "body").
"Pyrosomes are known to produce one of the most spectacular bioluminescent displays of any animal," explains Dave Bennet, one of the only marine biologists to actively study these animals in recent years.
As with many deep-sea inhabitants, it's thought the bioluminescence here acts as a warning, a smoke-and-mirror display to ward off would-be predators.
"Your prey suddenly glowing blindingly all around you is enough to scare most away," explains Bennet, adding that there is still a lot to learn about these little-studied organisms. For example, we still don't know just how their light organs actually work.
"Every time I tell another biologist what I’m studying they inevitably say ‘What? What’re they?'," he says.
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Top header image: Nick Hobgood/Flickr
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