Salps: Thaliacea

Physical characteristics: Individual pyrosomes (PYE-ruh-sohms) are about 0.3 inches (8 millimeters) long and are embedded in a thick, clear tube that forms the base for a colony as long as 24 inches (60 centimeters). Colonies are pink or yellowish pink. The mouth openings of the pyrosomes face out from the tube, and the water-exit holes point toward the inside of the colony. Pyrosomes produce light, which appears in waves of a brilliant glow along the colony.

Pyrosomes produce light, which appears in waves of a brilliant glow along the colony. (Illustration by Emily Damstra. Reproduced by permission.)

Geographic range: Pyrosomes live all over the world in warm to cool seas. Because they are found throughout the world, no distribution map is provided.

Habitat: Pyrosomes live in surface waters but each day travel down more than 2,500 feet (750 meters) and then return to the surface.

Diet: Pyrosomes eat plant plankton.

Behavior and reproduction: Water enters individual pyrosomes through the mouth holes and empties into the colony's common tube. The water exits the tube through an opening at one end of the colony, propelling the colony through the water. The water-pumping system also is used for feeding. Water entering each pyrosome passes through a mucus sheet that filters particles of plant plankton into the digestive system. Pyrosomes form swarms that produce huge amounts of feces.

Pyrosomes make both eggs and sperm. In each pyrosome of a colony a single egg is fertilized and then grows to a four-animal stage that leaves the parent to start a new colony by budding, which is a method of asexual reproduction by which a bump develops on an animal, grows to full size, and then breaks off to live as a new individual. This fast method of alternating asexual and sexual reproduction results in giant swarms of pyrosome colonies.

Pyrosomes and people: The brilliant light displays given off by colonies of pyrosomes have bewildered and fascinated sailors for generations.

Conservation status: Pyrosomes are not considered threatened or endangered. ∎