Phylum Annelida

Characteristics
Annelids were the first animals to evolve a complete coelom (an internal body cavity lined with epithelial tissue). They are segmented and have most comlete body systems.

Classification
Members of the class Polychaeta are marine worms. Members of the class Oligocheata are earthworms. Members of the class Hirudinea are parasitic worms.

Movement
Annelids have various muscle groups and simple appendages. They use setae and parapodia for movement.

Feeding & Digestion
Marine worms are filter feeders or scavengers. Earthworms squeeze organic material out of the earth. The digestive systems for all three classes are well-developed and use division of labor.

Circulation
Annelids are the first to have a closed system of blood vessels -- making pumping more efficient.

Excretion
Annelids have one pair of nephridia per segment for excretion.

Respiration
Respiration occurs through diffusion.

Nervous System
Members of this phylum have a simple brain located in the anterior end with ganglia in every segment. They can sense light, moisture, and chemicals.