How many pairs of hearts are found in earthworms (in $pairs$)?

Spermathecal pores of $Pheretima$ are present in

Following are the statements about the prostomium of an earthworm.
$(a)$ It serves as a covering for the mouth.
$(b)$ It helps to open cracks in the soil into which it can crawl.
$(c)$ It is one of the sensory structures.
$(d)$ It is the first body segment.
Choose the correct answer from the options given below.

In earthworms,setae are present in all segments,except the

In $Pheretima$, the number of ring vessels per segment in $12^{\text{th}}$ and $13^{\text{th}}$ segments is: (in $pairs$)

Which of the following statements is true regarding the earthworm?