Ectoprocta

The Columbia Encyclopedia, 6th ed.

Ectoprocta

Ectoprocta (ĕk´təprŏk´tə), phylum of sessile, colonial aquatic animals (commonly known as moss animals or oryonzoans). The zooids, or individual members of a colony, are microscopic, but colonies may grow up to 1 ft (30 cm) or more in diameter. Some colonies are erect and branching; others are thin, flat encrustations on rocks, seaweed, or water plants. The body wall of each zooid forms a tubular or boxlike case from which a circular or U-shaped crown of ciliated tentacles, the lophophore, is extended for feeding. Tentacle cilia generate water currents that sweep small organisms and organic particles toward the mouth, located within the lophophore. They reproduce sexually via a planktonic larval stage which settles and attaches to start a new colony. They also reproduce asexually by fission, fragmentation, or encapsulated resting stages. They were formerly placed in the phylum Bryozoa along with the Entoprocta, which they superficially resemble. Ectoprocts are a large and ancient group (dating from the Ordovician). There are about 5,000 living species.

Class Phylactolaemata

Exclusively freshwater animals having chitinous or gelatinous zooids with circular or horseshoe-shaped lophophores and well-developed body wall musculature. They produce characteristic resting bodies called statoblasts, which can survive cold and drying and germinate to found a new colony.

Class Stenolaemata

Fossil and recent marine animals that have tubular zooids, calcified walls, and circular orifices. Protrusion of the circular lophophore does not depend on muscular deformation of body walls. They reproduce sexually by embryonic fission (polyembrony).

Class Gymnolaemata

Fossil and recent primarily marine animals with cylindrical or boxlike chitinous or calcified zooids. Their colonies are often polymorphic, with zooids specialized for feeding, defense, support, and reproduction. The lophophore is circular and protrusion depends on body wall deformation.

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