Bryozoa. Light micrograph of Plumatella repens bryozoa. Plumatella is a freshwater colonial organism. Colonies are composed of individual zooids that secrete a mineralised shell, the zooecium, into which it can retract.Each zooid has a lophophore, a crown of tentacles lined with cilia, that are used to trap food particles from the water. Magnification: x16 when printed at 10 centimetres wide.