Bryozoans (Moss Animals)

Bryozoans, also known as Ectoprocta, are colonial aquatic invertebrates. A colony is built from anywhere from a few to millions of tiny zooids, each less than a millimeter long and enclosed in a sheath of tissue, the zooecium, that in many species secretes a rigid skeleton of calcium carbonate. Each zooid feeds with a lophophore, a ring of ciliated tentacles around the mouth, and the anus sits just outside it, which gives the name Ectoprocta, Greek for anus outside. Most living species encrust rocks and shells in flat sheets, while upright forms were much more common in the Paleozoic.