Question

Which one of the following exhibits an incompressible fluid within the body cavity against which muscles can do work for body movement?
A. Earthworm
B. Starfish
C. Euplectella
D. Jellyfish

Answer 1

Hint: Coeloms are fluid-filled cavities between the body wall and the digestive tract. The animals possessing coelom are coelomates. The coelomic fluid in the coelom acts as a simple circulatory system, transporting food, gases, and wastes around the body to provide space for the development of a true circulatory system. It cushions the suspended organs, helping to prevent internal injury. It also acts as a hydroskeleton in the soft-bodied animals.

Step by step answer:
The earthworm moves by crawling, in which its body remains on the ground. Crawling occurs by muscle contraction and extension of the body, aided by chitinous bristles, the steam, of the skin. Locomotion starts with the contraction of the circular muscles in a limited region of the anterior part of the body. The contraction makes the region thin and exerts pressure on the coelomic fluid contained therein. This pressure causes elongation of that region by relaxation of longitudinal muscles. This contraction of circular muscles passes backward over the body like a peristaltic wave so that thinning and elongation gradually affect more and more posterior segments.

Hence, the correct answer is option is A. Earthworm

Additional information:
Earthworm(Lumbricus terrestris) belongs to the phylum Annelida of the non-chordate animals. They are known by several names such as nightcrawlers, rainworms, fishing worms, angleworms, etc. It is a nocturnal animal.

Note: The presence of coelomic fluid helps the annelids help in locomotion and fluid regulation through their body walls.