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.
Members of the class Polychaeta are marine worms. Members of the class Oligocheata are earthworms. Members of the class Hirudinea are parasitic worms.
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.
Annelids are the first to have a closed system of blood vessels -- making pumping more efficient.
Annelids have one pair of nephridia per segment for excretion.
Respiration occurs through diffusion.
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.
Since annelids are hermaphroditic, sexual reproduction occurs through the exchange of sperm packets.