List of Types of Segmented Worms. Environmentally beneficial, earthworms help fertilize and aerate soil. Ryan McVay/Photodisc/Getty Images. Worms are invertebrates with long, soft bodies and no hard skeleton. Their shapes are varied, and they range in size from microscopic to 75 feet in length. Scientists have classified worms into more than 15 phyla. The phylum Annelida contains the segmented worms. Annelida is further divided into three subclasses: Oligochaeta, Hirudinea and Polychaeta. Thousands of species of segmented worms comprise these three subclasses.