Earthworms are also bilaterally symmetrical like flatworms, but instead of being flat, they are round in transverse section (widthways), as well as being segmented metamerically. Metameres are repeating sections in an organism that have the same structure, although may accomplish different functions based on their tissue distribution and specialisation.
For example, the gut is specialised between the metameres, and the earthworm has both a mouth and an anus for continuous digestion.
A hydrostatic skeleton is present, formed from the body cavities of each segment.
The prostomium is the first segment starting at the head. The clitellum is the egg-storing structure near the head, while setae are hair-like structures on the earthworm surface.