Bryozoans

Bryozoans, also known as moss animals, are a phylum of small, sessile, colonial aquatic invertebrates that filter feed using a lophophore, a crown of ciliated tentacles.

Most bryozoans form colonies composed of numerous zooids, each housed in a protective chamber called a zooecium, produced by the secretions of the colony. These colonies create a shared skeleton, usually calcareous in marine groups, forming sheets, branches, or other structures.

Within the colony, individual zooids are specialized for feeding, reproduction, or defense; some zooids called avicularia resemble beaks and can deter predators, while vibracula help keep the colony clean.

Reproduction occurs both asexually, by budding that expands the colony, and sexually, with fertilization producing free-swimming larvae that settle to form new colonies. In many freshwater bryozoans (Phylactolaemata), dormant statoblasts endure unfavorable conditions.

Taxonomy: Living bryozoans are divided into Phylactolaemata (freshwater) and Gymnolaemata (mostly marine), the latter including the diverse order Cheilostomatida, which dominates modern seas.

Ecology: Bryozoans are common epibionts on rocks, algae, shells, and man-made substrates; they are efficient filter feeders and contribute to habitat structure in some environments. They have a long fossil record and provide paleoenvironmental information.

Fossil record: Bryozoans first appear in the Early Ordovician and expanded greatly in the Paleozoic, leaving a rich calcitic skeleton that preserves well.

Significance: Their colonial organization, diverse morphologies, and extensive fossil record make them important for studies of evolution, ecology, and paleoecology.