Write the general characters of Annelida.  

Explanation

Annelida may be aquatic (marine and fresh water) or terrestrial, freeliving and sometimes parasitic.
They exhibit organ-system level of body organisation and bilateral symmetry.
They are triploblastic, metamerically segmented and coelomate animals.
Their body surface is distinctly marked out into segments or metameres and, hence, the phylum name Annelida. (Latin, annulus - little ring).
They possess longitudinal and circular muscles which help in locomotion.
Aquatic annelids like Nereis possess lateral appendages, parapodia, which help in swimming
A closed circulatory system is present.
Nephridia (sing, nephridium) help in osmoregulation and excretion.
Neural system consists of paired ganglia (sing. ganglion) connected by lateral nerves to a double ventral nerve cord.
Nereis, an aquatic form is dioecious, but earthworms and leeches are monoecious.
Reproduction is sexual.
Example : Nereis, Pheretima (Earthworm) and Hirudinaria (Blood sucking leech).