A hollow tube of thousands of linked tunicates, closed at one end, that glows when touched.
A pale translucent tube, open at one end and closed at the other, with a finely pimpled surface. Small ones look like a thimble; large ones are long enough to be mistaken for a discarded plastic sleeve. Held in the beam the surface resolves into thousands of tiny individuals set in a common jelly, which is the feature that separates it from a salp chain, where the individuals are visibly separate animals in a line.
A pyrosome is a colony, not an animal. Each zooid draws water in from the outside of the tube and expels it into the central cavity; the combined outflow from the closed end drives the whole colony slowly through the water, and the same current feeds every member. Colonies grow by budding and can reach several metres in some species, though what turns up on a blackwater dive in this region is usually hand-sized or smaller.
The name means fire body. Pyrosomes are strongly bioluminescent and respond to touch and to light, a blue-green glow that spreads across the colony from the point of stimulus and can persist for some seconds. This is genuine light production, unlike the diffraction that runs along a comb jelly’s comb rows, and it can be photographed, though it needs the focus light off and a good deal of patience.
Ratings are per location: 1 means found on most dives that look for it, 5 means a handful of records. Where enough dives have been logged the figure is calculated from them; otherwise it is an editorial estimate, and says so. We publish habitat and destination, not the dive site.
