Annelida
Characteristic of all Annelids is the fact that they are all, to some extent, segmented, with each portion of the Annelid containing important aspects of the major body systems. Annelids are also all bilaterally symmetrical animals, with their internal organs being protected by circular and longitudinal muscle fibers. Nearly all Annelids have fluid-filled cavity between the outer body and the gut called the coelom, which acts as both the storage area for the Annelids gametes, and a spongy skeleton that the Annelid braces against in order to move itself around. Because the coelom is segmented like the rest of the Annelid's body, the Annelid will be able to move around even if part of its body is injured, as copies of the coelom are present in each of the Annelid's segments. The internal body systems of Annelids are well developed, including a closed-circulatory system, a digestive system complete with mouth and anus, and a nervous system that runs along the belly.