In earthworms,pairs of hearts are located in which segments?

Which of the following is found in an earthworm?

The earthworm does not have a skeleton,but during burrowing,its posterior end becomes turgid and acts as a hydraulic skeleton. This is due to:

In $Pheretima$,there are red-coloured round bodies in the $4th$,$5th$,and $6th$ segments above the alimentary canal. They are believed to be involved in:

$A$: Earthworms have a closed type of circulatory system.
$R$: In earthworms,hemoglobin is dissolved in the blood plasma.

Identify the correct sequence of organs in the digestive system of an earthworm.