Stenolaemata, like bryozoans in general, are colonial animals, with many species superficially resembling seaweeds or corals. A common sort of stenolaemate colony consists of a branching array of hollow, calcified tubes, which serves as a skeleton, the tubes studded along the lengths of the tubes with individual, functional units called "zooids." Stenolaemate colonies can take a variety of forms, including crustlike, rosette, cup-shaped, branching, lumpy, and leaf-shaped. Colonies may bear calcified structures arising from the support skeleton, called "maculae," that function in colony hygiene, directing "used" water, or water already sifted for food particles and carrying wastes, away from the colony for hygiene purposes.
A single colony may be less than a millimeter high, or grow as high as a few feet (1 m) or more. The individual zooids are microscopic or nearly so. Microscopes are standard and necessary tools for studying and identifying bryozoans.
Stenolaemata zooids are characteristically elongated and cylindrical. Each zooid sits in a chamber called a "zoecium," encased in a calcified cystid for protection. Zooids within a single colony may differ considerably in form and function (polymorphism). Most numerous are the feeding zooids, or autozooids, each of which has a coelom, or inner body cavity, formed from the mesoderm, as well as a digestive tract, nervous system, and muscles. Although an autozooid feeds independently, it connects and communicates with the entire colony. Non-feeding zooids, or heterozooids, in Stenolaemata include gonozooids (reproductive) and kenozooids, which lack an internal organ system and serve as extra support for the colonial skeleton.
To feed, an autozooid extends an organ called a lophophore, consisting of a tentacle sheath and a ball of rolled-up, hollow tentacles. The tentacles open up into a graceful, flowerlike, bell-shaped structure. Cilia studding the tentacles draw currents of water into the mouth, to the center of the lophophore, and into the digestive tract and gut, with a caecum that grinds up food particles with peristaltic motions. The tract communicates directly, via pores, with another tract running the length of the supporting skeletal tube, allowing ingested food to be shared throughout the colony. A zooid passes its wastes through an anus, on the tentacle sheath below the tentacle ring.
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