|Pyrosoma atlanticum (Peron, 1804) : Pyrosome
Phylum Chordata / Subphylum Urochordata / Class Thaliacea / Order Pyrosomatida / Family Pyrosomatidae
The pyrosomes include a variety of colonial pelagic tunicates. Most species inhabit tropical waters, with some up to 4 meters in length. Pyrosoma atlanticum is one of the few pyrosomes that visits the temperate West Coast. The colony may reach a length of 60 cm and forms a distinctive rigid tube that may be colorless, pink, grayish or blue-green. One end is closed and tapered, with the opposing open end having a diaphragm. The tube has a rough texture due to papillae on the individuals making up the colony. Each individual has a large branchial sac with many gill slits, along which runs the mucus secreting endostyle. Unlike salps that use pulsing of the body wall to pump water, pyrosomes depend on cilia to move water through the body. This enables planktonic food to be collected by mucus filters within each individual, and also provides the propulsive force for locomotion of the colony.
Like other pyrosomes, this species is brightly bioluminescent, producing an intense blue-green glow when disturbed. It may range for up to 800 vertical meters during daily migrations. While not common in Monterey Bay, Pyrosoma atlanticum is the most widespread and abundant pyrosome in temperate and tropical waters of all oceans. With its distinctive characteristics, it is unlikely to be confused with any other gelatinous visitor to California nearshore waters. The genus name (Pyrosoma) is derived from the Greek, pyros (fire) and soma (body), referring to the bright bioluminescence characteristic of this group.