Insects Insects are neumerout invertebrate animals that belong in the Phylum Arthropoda and Class Insecta. The class Insecta is divided into 2 subclasses: Apterygota, or wingless insects, and Pterygota, or winged insects. Subclass Pterygota is futher divided on basis of metamorphosis. Insects that have undergone incomplete metamorphosis are the Exopterygota. Insects that undergo complete metamorphosis are the Endopterygota. Insects have an outer bilateral exoskeleton to which the muscles are attached to and provides protection for internal organs. The body is divided into 3 main parts which are the head, which include mouthparts, eyes, and antennae; thorax, which operate the jointed legs and /or wings;