This is the first of three volumes dedicated to animals that molt in the course of their lifecycle, the Ecdysozoa. It covers all non-hexapods and non-crustaceans, i.e., the Cycloneuralia, Tardigrada, Onychophora, Chelicerata and Myriapoda. While the Nematoda and all other phyla are treated in their own chapters, the remaining cycloneuralians are presented jointly due to the dearth of available developmental data on its individual subclades.