Internal Anatomy of an Earthworm An annelid of the oligochaete class, the earthworm shows the well-developed segmentation that is characteristic of its phylum. Although the major nervous, circulatory, and digestive organs are located near the head, more posterior segments contain peripheral structures for all of these systems. These posterior segments are virtually identical to each other. Earthworms are hermaphroditic, possessing both male and female internal reproductive organs.

Earthworms have no eyes, ears, or lungs. They breathe when air that is present between soil particles diffuses through their thin skins, and they are forced to the surface if these air pockets fill with rainwater. When a worm moves, it uses its longitudinal muscles to extend the front of its body into the soil ahead of it, pulling the back part up behind it. Setae, tiny projections from each segment of the worm, stick into the surrounding soil to keep the worm from slipping.