Ectoprocta

Ectoprocta (ek"tuprok'tu) [key], 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.

The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2007, Columbia University Press. All rights reserved.

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