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Most people walk past pyrosomes on beaches or see videos of scuba divers swimming through them and think they are some kind of massive jellyfish, a giant sack of eggs, or a weird mutant cucumber. However, they’re actually a colony of thousands of individual organisms called tunicates!

There exists a single “original” tunicate, and the rest of the tube is made up of thousands of genetic clones that are built over time. They all live inside a single gelatinous tunic and connect within it, sharing a common water intake/exhaust system. Each individual zooid pulls water in, filters out plankton for food, and pushes the filtered water back out into the central tube. That collective exhaust builds and acts like a jet propulsion system, slowly moving the whole giant colony through the water. How cool is that?!

They are also intensely bioluminescent through a chemical reaction known as the “Luciferin-Luciferase reaction”. A specialized enzyme (luciferin) oxidizes a light-emitting compound (luciferase) inside small light-producing cells located on each zooid. If you touch one or stimulate the pyrosome with light, it triggers a chain reaction that passes the signal to neighboring cells, creating a wave of blue-green light across the entire colony. Divers have called swimming inside a hollow pyrosome tube “swimming through a tunnel of stars.”

What are some of your favorite aquatic weirdos?