Salpae

Salpae 

(also Desmomyaria), a subclass of free-swimming marine animals of the subphylum Tunicata. Salpae live mainly in surface waters of the ocean; they are found to depths of several hundred meters. The cylindrical body ranges in length from a few millimeters to 33 cm and is covered with a transparent tunic, through which are visible the gut and ribbons of annular muscles. At opposite ends of the body are siphonal openings—the cloaca and the mouth, which leads to a large pharynx. The heart is on the ventral side, and the circulatory system is open. The nervous system is a suprapharyngeal ganglion from which nerves depart. Above the ganglion is a photosensitive organ known as the ocellus.

There are about 25 species of Salpae, inhabiting all the oceans except the Arctic Ocean. The life cycle involves the alternation of sexual and asexual generations. A single embryo develops in the body of a hermaphroditic individual. The young animal that emerges from the egg into the water has an appendage, the stolon, on which bud numerous individuals of the sexual generation. Chains of the organisms break off from the stolon and exist in the form of colonies including as many as several hundred individuals. Sometimes Salpae form extensive aggregates in the ocean. The animals are luminous owing to the presence of symbiotic bacteria. Salpae feed on phytoplankton and serve as food for certain fishes and marine turtles.

G. M. BELIAEV