If you’re looking for a strange sea creature, you can’t get much weirder than the giant pyrosome. With an appearance like a monster out of a science fiction movie, those who’ve had the good luck to see them have likened them to everything from unicorns, due to their rareness, to the Borg, because of how they stick together and seem to be part of a collective.
Pyrosomes are often referred to as “corn cob jelly,” but they are not really jellyfish. They are urochordates, an animal group that is ancestral to chordates, or animals with backbones. The most important thing to understand about the giant pyrosome is that it’s not a single organism. It is in fact sometimes hundreds of thousands tiny, “cloned” organisms, called zooids, linked together in a gelatinous “tunic.” The zooids arrange themselves in a tube that’s hollow at one end, with each zooid’s head poking out of the gelatin along all sides of the tube to facilitate feeding. Although individual zooids are only a millimeter or two in size, pyrosome colonies can grow to up to several meters. Perhaps one reason they are rarely seen is that they most commonly live in the open oceans and rarely come close to shore.
Aside from their apparently menacing, sea monster-like appearance, what seems to fascinate most people about the giant pyrosomes is how they move: like a jet engine. While cephalopods, like octopi and squid, may ingest and expel water to “jet” themselves forward, only pyrosomes do it in a completely continuous way. Pyrosomes are filter eaters, which means they eat plankton. Each zooid takes water into its mouth with cilia, filters out the food in its stomach, and then expels the water into the empty center of the tube. The constant inflow of water into the tube’s center displaces water out the open end and so pushes the organism forward. While the speed isn’t much, barely a crawl, it is remarkable how it’s produced by the thousands of zooids working together, all while eating. Mostly, however, even the largest pyrosomes are so light and live so near the ocean’s surface that their positions and movements are really the result of whatever current is at work at the time.
If their name hasn’t already given you a hint (pyro = “fire” and soma = “body”), pyrosomes exhibit bioluminescence. While certainly not the only sea organism to produce light, scientists find the pale-blue pyrosome light particularly fascinating because of its brilliance and long lastingness. Also, individual zooids not only produce the light, but they also seem to “send” it to the other zooids around them, making the light appear to spread like a “wave” through the colony and even to neighboring colonies. It’s this collective form of bioluminescence that really sets the pyrosomes apart from other light-producing sea creatures. While the phenomenon of bioluminescence itself may not be that beneficial to us, as biologist David Bennett has pointed out, studying it has led to a “wide variety of laboratory techniques” that are “helping scientists to discover many new phenomena, and aid development of treatments for many diseases.” One indication of how seriously scientists now consider the study of bioluminescence is that the 2008 Nobel Prize in Chemistry was awarded to a group of chemists in recognition for their discovery and development of the green fluorescent protein GFP.
If you read anything else about giant pyrosomes, you’ll probably read something about how they “may look menacing,” but are in fact “soft and gentle” giants. They are indeed quite light, and have been described as “soft and fluffy” by those who have actually been able to feel them, but you might want to hold off from thinking they’re completely harmless. One diver reported finding a two-meter long pyrosome with a dead penguin stuck in it! Apparently, the penguin mistakenly had swum into the open end of the pyrosome and couldn’t get lose. Penguins are not weak birds, so it’s clear that the giant pyrosome can “pack a pretty good punch” itself.
More to Explore
Giant Pyrosome and Salps
Tunicates – Salps, Doliolids, and Pyrosomes
Pictured: The Incredible Deep-sea Glow Worm Called the ‘Unicorn of the Sea’ that Can Grow Up to 100ft
12 Reasons Why Pyrosomes Are My New Favorite Terrifying Sea Creatures
The Pyrosome Story
While BioZine is on summer vacation, we hope you enjoy this article from the archives. This article was first published in March 2014.