The members of the phylum Bryozoa are almost exclusively colonial invertebrates, being comprised of small individual zooids growing in many different shapes such as runners, sheets, mounts, plates or trees. They are often mistaken for corals, sponges or even seaweeds. Bryozoan colonies arise from numerous asexually proliferated zooids. Each zooid is enclosed in a protective box-like exoskeleton, with apertures for ciliated feeding structures known as lophophores. Bryozoa are sessile suspension feeders.
Bryozoans have been discovered in great numbers and in an amazing diversity of morphological forms in the deep-sea. There are some large forms but most are small, fragile and rarely collected intact. Bryozoans can be rigid, with fused zooids forming strong erect branched forms. Soft ctenostome forms lack a rigid calcified skeleton. Ctenostome bryozoans are normally found on abyssal mud and illustrate how bryozoans have adapted to the deep-sea environment.