1. Body long, cylindrical, bilaterally symmetrical and with true cylomes.
2. The body is segmented and composed of many segments or metameres similar to rings.
3. Movement organs are chitinous seatae or parapodia.
4. Patchy excretory organs called nephridia are located in almost every segment. It is called segmental organ.
5. The body contains the clitellum and secretes mucus.
6. The alimentary canal is cylindrical and complete and consists of oral and anal openings.
7. Blood is red. Plasma contains hemoglobin, heme-erythrin or chloroquine.
8. The body is composed of chitinless and soft cuticle.
9. The larval stage of the life cycle consists of trochophores.
10. They are unisexual or bisexual. Reproduction occurs sexually and asexually.