Question

The first body segment of earthworm is
A.Peristome
B.Peristomium
C.Protostomium
D.Protostome

Answer 1

Hint: Earthworm is an invertebrate. It has a tube within a tube body plan. They occur worldwide. They are commonly found in soil, eats organic matter. Earthworms are hermaphrodites that mean they have both male and female sexual organs.

Complete answer:
1.The Earthworm consists of about 100-150 segments. Segmentation helps the earthworm to move.
2.The earthworms are bilaterally symmetrical. The earthworm is divided into a series of segments. Each segments carry bristle like hairs called lateral setae except for mouth and anal segments. Setae are used to anchor parts of the body during movement.
3.The first body segment in an annelid worm’s body is called peristomium. It is behind the prostomium and contains the mouth. The prostomium is in front of mouth, usually a small shelf like extension over dorsal side of mouth.
4.Earthworms lack a true skeleton, maintaining their structure with fluid filled coelom chambers that function as a hydrostatic skeleton.
5.An adult earthworm has a belt shaped glandular swelling which is known as clitellum and it covers the several segments towards the front part of the animal.
6.The last segment is called a periproject. In this segment, the earthworm’s anus, a short vertical slit is found.
7.Septa separate the segments from each other. Septa are perforated transverse walls and allow the coelomic fluid to pass between segments.

Hence the correct answer is OPTION(B)

Note: The periosteum and prostomium can be fused by distinct or comprising a joint structure of a peristomial ring and a tentacular crown. Prostomium is a small fleshy lobe that overhangs the mouth of an earthworm. In front of the mouth portion of the head of annelids is situated called Prostomium.