Giant Pyrosomes are bioluminescent (light producing), giving rise to the common name, which comes from the Greek for fire (“pyro”) and body (“soma”). The light produced by Giant Pyrosomes is particularly bright and long lasting and is beautiful to witness. Because the individual tunicates can reproduce via cloning, the colony can regenerate injured parts or continue growing after being broken apart. Unless all individual clones are killed at the same time, a colony can theoretically live forever, shrinking and growing based on available food and physical disturbance. Individual clones are hermaphroditic; they make both eggs and sperm. When two colonies meet in the open ocean, individuals likely engage in sexual reproduction. The colonies also reproduce asexually, by budding off tiny starter colonies that contain a few individual clones. Giant Pyrosomes are closely related to other pelagic tunicates (such as the salps) and more distantly related to benthic tunicates (called ascidians) and vertebrates.
Each zooid is 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, although perforated with holes for each zooid, on the inside
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.
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
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