Question

Setae are found in all body segments of earthworm except
A. Last segment
B. First segment
C. Clitellar segment
D. First, last and clitellar segments

Answer 1

Hint: Setae are S-shaped chitinous structures present in the segments of earthworm. These are 80-120 in number per segment. These help in locomotion and copulation.

Complete answer:
Earthworms are formed of 100-120 segments called metameres or somites, due to the presence of ring-like grooves called annuli. They show metameric segmentation i.e. the external division of the body corresponds with the internal segmentation of the body. The first segment is called the periosteum or buccal segment.
They show creeping type of locomotion with the help of contraction and relaxation of body muscles. It is aided by setae and coelomic fluid.
The simultaneous contraction of circular muscles and relaxation of longitudinal muscles of a few segments make that part to lengthen.
The setae are protruded and embedded in the soil to anchor that part. Now the circular muscles relax and longitudinal muscles contract which make that part to shorten and pull the posterior part.
This wave of contraction and relaxation extends anteroposteriorly.
These setae are present in all the segments in a perichaetine arrangement except the first, last and clitellar segments.
Clitellum is the glandular collar like thickening that surrounds the 14th, 15th and 16th segments. It forms ootheca or cocoon during the breeding season and is also absent in the immature worm. So these segments are called the clitellar segments in the earthworm.

So, the correct option is D.

Note: Earthworms are terrestrial and fossorial annelids found in soft and moist soil of gardens and lawns that are rich in dead plant materials.