Class Polychaeta: Polychaetes as a class are robust and widespread, with species that live in the coldest ocean temperatures to forms which tolerate the extreme high temperatures. They tend to eat the soil around them, and they also have segmented bodies.
Class Oligochaeta: This class includes about 3,500 species of earthworms and freshwater worms. Oligochaetes occur in a variety of habitats throughout the world. Most are burrowers in the soil, but the class also includes worms that inhabit wells, marshes, and swamps. The Oligochaetes tend to eat the soil and some small plants around them.
Class Hirudinea: This class includes the 500 species of leeches, flattened, predacious or parasitic annelids equipped with suckers used for creeping. Leeches are primarily freshwater annelids, but some live in the ocean and some in moist soil or vegetation. The majority of leeches are predators on small invertebrates; most swallow their prey whole, but some suck the soft parts from their victims