Explain the external structure of an Earthworm with a diagram.

(N/A) $\Rightarrow$ Earthworm is a reddish-brown terrestrial invertebrate.
$\Rightarrow$ It inhabits the upper layer of moist soil.
$\Rightarrow$ During the daytime,they live in burrows made by boring and swallowing the soil.
$\Rightarrow$ In gardens,they can be traced by their faecal deposits known as worm castings.
$\Rightarrow$ The common Indian earthworms are $Pheretima$ and $Lumbricus$.
$\Rightarrow$ The earthworm is a coelomate animal belonging to the phylum $Annelida$.
$\Rightarrow$ Earthworms have a long,cylindrical body.
$\Rightarrow$ The body is divided into $100-120$ short segments. Its length is approximately $15 \ cm$.
$\Rightarrow$ The dorsal surface of the body is marked by a dark median mid-dorsal line (dorsal blood vessel) along the longitudinal axis.
$\Rightarrow$ The anterior end consists of the mouth and the prostomium.
$\Rightarrow$ The prostomium is a lobe which serves as a covering for the mouth and as a wedge to force open cracks in the soil.
$\Rightarrow$ The first body segment is called the peristomium.
$\Rightarrow$ The body has no specific head. The mouth is semilunar in shape,and the anus is at the posterior end.
$\Rightarrow$ In a mature worm,segments $14-16$ are covered by a prominent dark band of glandular tissue called the clitellum.
$\Rightarrow$ The body is divisible into three regions: preclitellar,clitellar,and postclitellar segments.
$\Rightarrow$ The ventral surface is distinguished by the presence of genital openings.
$\Rightarrow$ Four pairs of spermathecal apertures are situated on the ventro-lateral sides of the intersegmental grooves,i.e.,between segments $5-9$.
$\Rightarrow$ $A$ single female genital pore is present in the mid-ventral line of the $14^{th}$ segment.
$\Rightarrow$ $A$ pair of male genital pores are present on the ventrolateral sides of the $18^{th}$ segment.
$\Rightarrow$ Genital papillae are located on the ventrolateral sides in the $17^{th}$ and $19^{th}$ segments.
$\Rightarrow$ Numerous minute pores called nephridiopores open on the surface of the body.
$\Rightarrow$ In each body segment,except the first,last,and clitellum,there are rows of $S$-shaped setae,embedded in epidermal pits.
$\Rightarrow$ Setae are helpful in obtaining a grip in the soil and play an important role in locomotion.