Giant Fire Pyrosome, Pyrostremma spinosum

Pyrosomes of the Pyrosomatidae Family, like humans and other complex organisms, are in the Phylum Chordata. This means that they have a notochord (a primitive spine), a dorsal, tubular, nerve chord, a post-anal tail, and pharyngeal slits (filter feeding organs). In many animals, these traits are only present during their embryonic or larval stage of development. For example, in humans the pharyngeal slits are only present during the embryonic stage of development and transition to form the jaw and inner ear structures, the tail disappears completely. In bony fish the Pharyngeal slits transition to form the gill arches. Pyrosomes are in the Subphylum Tunicata, that is also known as Urochordata. Tunicate larvae are tadpole-like and display all of the Chordate traits. As they metamorphose, they lose their spine, tail, and nervous system. They retain their filter feeding abilities. Adult tunicates are essentially sack-like, with 2 openings (siphons). Water flows in one siphon, is filtered through the body, and flows out the other siphon. Tunicates maybe sessile or pelagic. Salps and Sea Squirts are also included in this subphylum.

Pyrosomes are in the Class Thaliacea. Thaliacea are pelagic tunicates, in which, the 2 siphons are at opposite ends of the body. Flexing of the body wall and cilia move water through the siphons. This water movement is used for respiration, feeding, waste removal, and limited propulsion. This propulsion is primarily used for daily vertical migration. Thaliacea spend the day in deep water and ascend to the surface at night for feeding. Otherwise, they drift with the currents and are considered plankton. Thaliacea have a transparent test (gelatinous body covering). They may be solitary or colonial.

Pyrosomes are in the Order Pyrosomatida. They are colonial tunicates, made up of individuals known as zooids. The zooids are held together within the test. The intake siphon of individual zooids opens on the external side of the body wall. The outflow siphon opens on the interior wall. This design builds pressure inside the body sack, which is released though the open end, providing propulsion. Family members are known for their bright bioluminescent flashes. Pyro soma means, ”fire body”, and is in reference to this trait. They are also characterized by their reproductive cycle that alternates between sexual and asexual generations. There is only the Pyrosomatidae Family, and three genera in this Order. The Pyrosomatidae Family has 8 known species of which at least 3 are found along Mexico’s Pacific Coast. Very little is known about the geographic distribution of these species.

Pyrosomes may reach up to 20 m (65 feet) in length. They feed on phytoplankton that they filter from the ambient water. In turn they are preyed upon by fish, sea birds, sea turtles, whales and other plankton. They are found worldwide, in temperate and tropical waters.