According to Nature Watch, the earthworm does not have a backbone and therefore has no skeleton. This segmented creature is classified as an invertebrate. The earthworm is composed of a mucous-like epidermis and various segments that help define its structure.
Earthworms usually consist of at least two main segments, the peristomium and the periproct. The peristomium is the first segment on an earthworm's body that includes the mouth. The periproct is located on the posterior end of an earthworm. A distinctive swelling called the clitellum, which is only found on sexually mature earthworms, lies between the two main segments. To identify a specific species of an earthworm, look for glandular swellings located on the sides of the clitellum called tubercula pubertatis. The location and appearance of these swellings differ in various species of mature earthworms.