Entoprocta

Entoprocta A phylum of small invertebrate aquatic animals typically having a cup-shaped body bearing tentacles and attached to the substrate by means of a stalk. The entire animal is usually less than 10 mm long. There are about 150 known species, widely distributed and almost exclusively marine. Many species are colonial and form mats on seaweeds, rocks, shells, and other surfaces in coastal waters. Each individual has a ring of 4–36 ciliated tentacles (calyx) on top of the body, enclosing both the mouth and anus. The tentacles set up a feeding current and trap minute plankton and other particles in mucus, transferring the particles to the mouth. Digestion occurs in the U-shaped gut and waste is discharged via the anus. There is no heart or blood vessels, and the nervous system consists of a single ganglion between the mouth and anus, from which nerves extend to the tentacles, body, and stalk. Dissolved nitrogenous waste is discharged by exocytosis from the stomach wall into the gut, and also collected by a ciliated flame cell, and discharged via pores. Reproduction is both asexual, by budding, and sexual. Most entoprocts are hermaphrodites, and produce free-swimming larvae that settle on a substrate before undergoing metamorphosis into the sessile adult form. The space between the body wall and the gut is filled with a jelly-like mesenchyme; this has been interpreted by some as a pseudocoelom, prompting the suggestion that entoprocts are allied with other pseudocoelomate animals, such as nematodes. Others argue that developmental similarities between entoprocts and bryozoans (see Bryozoa) point to a close relationship between these two groups.