bryozoans, also known as the polyzoa, ectoprocta or moss animals, are a phylum of small aquatic animals living in colonies. the colonies usually have a skeleton of calcium carbonate. bryozoans have a long fossil history, starting in the ordovician. in their life-style they resemble the polyps which form coral. they generally like warm, tropical waters but live all over the world. there are about 5,000 living species, and 15,000 fossil species are known.