Write the general characters of Phylum Annelida.

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