Question

In Earthworms, the mouth is situated on
(a) Prostomium
(b) Peristomium
(c) Stomium
(d) Protostomium

Answer 1

Hint: Earthworm comes under the phylum Annelida and it is metamerically segmented with around 120-150 segments. The first segment of earthworm consists of an anterior end with a crescentic opening with the presence of a fleshy lobe.

Complete answer:
The first segment of earthworm consists of the periosteum which is an anterior end where a crescentic opening is present called mouth.
The earthworm is a nocturnal animal that is mainly active in the rainy season. In the day time, it rests in the burrow and at night it feeds and mates. It is borrowed by pushing the body in soil and the entrance gets covered by faecal casting, pebbles and leaves to keep water and enemies out. It shows locomotion with the help of setae and feeds on plant and animal matter therefore they are omnivorous. The food of earthworm gets digested in the gut and the undigested matter passes out in the form of small pills called worm castings which form heaps on the soil. It is also known as protandrous which means male sex organs mature earlier than female, therefore cross-fertilization takes place in them. Cross-fertilization takes place on the ventral surface where the head of one is opposite to the tail region of the other. When the earthworm gets irritated, it leads to the ejection of foul-smelling coelomic fluid through dorsal pores and after getting injured or getting cut into two pieces they don't die and show the power of regeneration.

So, the correct answer is 'Peristomium'.

Note:
The prostomium is present over the mouth as an overhanging fleshy lobe and it is sensory in function. It helps to detect the intensity and duration of light because earthworms do not have other sensory parts like the eye, ear and nose.