Carchesium a colonial peritrich similar to Zoothamnium but Carchesium is distinguished by zooids with discontinuous myonemes allowing individuals of the branched colony to contract independently. However, as seen in this image, the entire colony may contract simultaneously. The stalk of Carchesium contracts in a spiral configuration, seen in this image, unlike Zoothamnium and Pseudocarchesium whose stalks are described as contracting in a zig-zag fashion. Pseudocarchesium also has discontinuous myonemes. From a freshwater pond near Boise, Idaho. Brightfield.