‘Ecdysozoa: insects and nematodes’ explains how DNA sequencing has resulted in two very different phyla — arthropods (insects) and nematodes (roundworms) — belonging to the same superphylum. Although surprising due to their dissimilar anatomy, all these animals have one fundamental character in common — they shed their skins as they grow. The orders and classes of the vast Arthropoda phylum are described, showing the characteristics of an exoskeleton and segmentation. The evolution of flight is also highlighted. Smaller phyla such as the microscopic tardigrades and the forest-dwelling onychophorans, as well as the unusual internal structure of nematodes and their lack of segmentation are detailed.