Physical characteristics

Freshwater bryozoans appear in a variety of forms. The most conspicuous colonies are large, gelatinous masses, but other species are small, moss-like growths or patches of branching tubules. At the microscopic level the basic design is the same: every colony is composed of many identical zooids the anatomical features of which are devoted mostly to feeding and digestion. A horseshoe-shaped lophophore of ciliated tentacles (lophophore shape is circular in Fredericellidae) generates a current of water that draws suspended food particles toward the mouth. An elongated U-shaped gut mixes and digests the food then packs undigested particles into small pellets, which are expelled through the anus. Circular muscles within the colony wall maintain slight hydrostatic pressure, which enables the feeding apparatus to project into the water while long retractor muscles pull the lophophore unit back into the colony interior. Each zooid has a single nerve ganglion between mouth and anus, and nerve tracts extend into the lophophore and to the gut. No nerves pass between zooids. A cord of tissue called a funiculus connects the tip of the gut to the inner colony wall and functions in sexual and asexual reproduction. Each zooid is capable of budding additional zooids and forming dormant statoblasts.

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