Pyrosomes are cylindrical or cone-shaped colonies made up of hundreds to thousands of individuals, known as zooids. Colonies range in size from less than one centimeter to several metres in length. They are commonly called “sea pickles”.[1][2]
Each zooid is a few millimetres in size, but is embedded in a common gelatinous tunic that joins all of the individuals.[1]
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, although perforated with holes for each zooid, on the inside.[citation needed]
Pyrosomes are planktonic, which means 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.[citation needed]
Pyrosomes are brightly bioluminescent, flashing a pale blue-green light that can be seen for many tens of metres. The name Pyrosoma comes from the Greek (pyro = “fire”, soma = “body”). Pyrosomes are closely related to salps, and are sometimes called “fire salps”. Sailors on the ocean occasionally observe calm seas containing many pyrosomes, all luminescing on a dark night.[citation needed]
Bioluminescence
Although many planktonic organisms are bioluminescent, pyrosome bioluminescence is unusual in its brilliance and sustained light emission,[3] and evoked the following comment when seen by the eminent scientist Thomas Huxley at sea:
“I have just watched the moon set in all her glory, and looked at those lesser moons, the beautiful Pyrosoma, shining like white-hot cylinders in the water” (T.H. Huxley, 1849).[4]
Pyrosomes often exhibit waves of light passing back and forth through the colony, as each individual zooid detects light and then emits light in response.
Each zooid contains a pair of light organs located near the outside surface of the tunic, which are packed with luminescent organelles that may be intracellular bioluminescent bacteria.
The waves of bioluminescence that move within a colony are apparently not propagated by neurons, but by a photic stimulation process.[5]
Flashing zooids not only stimulate other zooids within the colony to bioluminesce, but nearby colonies will also display bioluminescence in response.
Colonies will bioluminesce in response to mechanical stimulation (touch), as well as to light.[3]
Resembles a giant string of coagulated spunk floating in Bryan Singer’s Twink party hot tub.