Bryozoans are microscopic aquatic invertebrates that live in colonies. The colonies of different species take different forms, building exoskeletons (outer protective structures) similar to those of corals. Most colonies are attached to a structure such as a rock or submerged branch. Freshwater bryozoans' exoskeletons are gelatinous (like jelly) or chitinous (like the "shells" of insects). Therefore, some colonies take the form of rounded, jellylike masses, while others resemble antlers or mosses (bryophyte means “moss animal”), or trace delicately like vines across rocks, or create furry-looking colonies. The species that creates the round, jellylike masses most often seen in Missouri is Pectinatella magnifica.
With enough magnification, you can see tiny individual bryozoans (zooids). Each zooid is attached to a surface at its base. Its body has an outer sleevelike structure (a cystid) and a mass of organs (a polypide) that moves within it. An opening at the top of the cystid permits the polypide to slide outward toward the water, exposing a headlike structure (lophophore) crowned with tentacles, which filter food from water. At the slightest disturbance, the polypide and tentacles retract instantly.