Divers have captured images of the rare giant pyrosome Pyrostremma spinosum (with the old name Unicorn of the Sea) in open water off the coast of Tasmania. Pyrosomes are colonies of tiny animals that form hollow tubes sealed at one end that can reach 30m in length! Watch the video…
Pyrosomes and salps are pelagic (free-swimming) tunicates or sea squirts. All species are open ocean animals that rarely come close to shore, and all are colonial, although many salps can also be solitary.
According to Friendly Neighborhood Marine Biologist – Emily, Unicorn of the Sea name change:
“I have to respectfully disagree with your claim that Pyrosomes are the unicorns of the sea. I say they are actually fluorescent cheetos of the sea, especially when they are near the surface.”
Pyrosomes, genus Pyrosoma, are free-floating colonial tunicates that live usually in the upper layers of the open ocean in warm seas, although some may be found at greater depths. Pyrosomes are cylindrical or conical shaped colonies made up of hundreds to thousands of individuals, known as zooids. Colonies range in size from less than one cm to several metres in length.
Each zooid is only a few millimetres in size, but is embedded in a common gelatinous tunic that joins all of the individuals. Each zooid opens both to the inside and outside of the “tube”, drawing in ocean water from the outside to its internal filtering mesh called the branchial basket, extracting the microscopic plant cells on which it feeds, and then expelling the filtered water to the inside of the cylinder of the colony. The colony is bumpy on the outside, each bump representing a single zooid, but nearly smooth, though perforated with holes for each zooid, on the inside.
Image © wikipedia
Pyrosomes are planktonic, which means that their movements are largely controlled by currents, tides and waves in the oceans. On a smaller scale, however, each colony can move itself slowly by the process of jet propulsion, created by the coordinated beating of cilia in the branchial baskets of all the zooids, which also create feeding currents.