Ectoprocta

Ectoprocta, commonly called bryozoans or moss animals, are a phylum of small aquatic invertebrates. Most species are colonial and sessile, attaching to rocks, seaweed, or shells. Colonies consist of numerous zooids housed in protective chambers called zooecia. Growth occurs by budding, producing encrusting sheets, branched networks, or erect fronds. The skeleton is usually calcium carbonate in marine groups; freshwater phylactolaemates generally have a non-calcified covering.

Each zooid contains a saclike body with a U-shaped gut and a lophophore, a crown of ciliated tentacles used for feeding. Water currents are generated by cilia, allowing capture of small particles. The soft tissues (polypide) can retract into the cystid for protection.

Reproduction occurs both sexually and asexually. Asexual budding adds zooids to colonies. Many colonies are hermaphroditic; others are dioecious. Fertilized eggs develop into free-swimming larvae (often cyphonautes in some groups) that settle to form new colonies. Freshwater phylactolaemates produce statoblasts, dormant cysts used for dispersal.

Ecology and fossil record: Bryozoans contribute to habitat complexity in marine and freshwater communities. Their skeletons are common in the fossil record, especially in Paleozoic rocks, and have aided paleoenvironmental interpretation. Diversity is greatest among Gymnolaemata, particularly the marine Cheilostomatida.

Systematics: Ectoprocta is an older term frequently used synonymously with Bryozoa. In modern classifications Bryozoa is the phylum within Lophotrochozoa; Entoprocta is a separate phylum. Bryozoans are characterized by the lophophore and a U-shaped gut with the anus outside the lophophore region.