Annelids

There are three classes of annelid worms: Earthworms (Oligochaeta) , Leeches (Hirudinea), and Polychaetes (Polychaeta).

The earthworms (Oligochaeta) habit of ingesting dirt particles while scavenging for organic matter makes them valuable tillers of the soil.

Earthworm segmentation is extensive and obvious. Internal partitions define individual coelomic chambers, that are filled with fluid to provide a hydrostatic skeleton. Paired nephridia occur in nearly every segment. The digestive system is complete. The circulation is closed. Two adjoining nerve cords extend from anterior to posterior. They bear few setae.

Leeches (Hirudinea) are aquatic or semiaquatic predators of invertebrates or parasites of vertebrates. Most have sharp jaws and less obvious body segmentation than the other two classes. Leeches have suckers at both ends of the body.

Polychaetes (Polychaeta) include wandering or tube-dwelling marine worms with tentacles and numerous setae. Polychaetes have fleshy appendages called parapods.

REVIEW: _____ have a coelom and pronounced segmentation, and a dizzying variety of modifications to the segments.
Answer annelids