Annelida
Structures
The Annelida has a closed circulatory system, and they are hermaphrodites.
Classes
Oligochaetes - Earthworms and aquatic species (have few chaeta)
Polychaetes - mostly marine species, each segment has a pair of parapodia which are paddle like feet that are used in locomotion and gas exchange.
Hirudinea - also known as leeches are predators that feed on invertebrates and others are parasites that suck blood, they secrete an anesthetic t0 prevent detection of the incision on the host, they also secrete hirudin which prevents blood from clotting during feeding.