Annelida:

Organization:  Organ level

Symmetry:  Bilateral

Coelom:  present (coelomates)

Segmentation:  Present

Arrangement of embryonic layers: Triploblastic

Digestive system:  Complete

Circulatory system:  Present

Respiratory system:  Absent

Habitat:  Free-living, marine, terrestrial and parasitic.

Sexuality: Hermaphrodite

 Notochord: Absent

 Reproduction:  Sexual by fusion of gametes and asexual by budding.

Fertilization:  Internal and external (indirect)

Excretory organ:  Nephridia helps in excretion and osmo-regulation.

Distinctive features:

• They possess longitudinal and circular muscles which help in locomotion.
•  Aquatic forms possess lateral appendages, parapodia, which help in swimming. Neural system consists of paired ganglia.
• Nereis, an aquatic form, is dioecious, but earthworms and leeches are monoecious.