Question

A skeleton like function during locomotion of Pheretima posthuma is performed by

• A. Blood
• B. Alimentary canal laden with mud
• C. Coelomic fluid
• D. Ventral nerve cord

Answer 1

Answer: (C)

Coelomic fluid

• A skeleton-like function during locomotion of Pheretima posthuma is performed by the movement of the coelomic fluid. The coelomic fluid acts as a skeleton which allows the earthworm to move forward and backward. The locomotion is brought about by an increase in the hydrostatic pressure of the anterior ten segments.
• There is the contraction of the circular muscles which begins at the anterior end and the wave passes backward. This causes the anterior region to extend forward. The anterior end grips and setae act as anchors on the soil.
• Then, the circular muscles relax and longitudinal muscles of the anterior segments contract in a wave beginning from the anterior end, which shortens the anterior end and causes the posterior part of the body to pull forward.
• These movements of contraction and relaxation results in the locomotory movement. The coelomic fluid serves as a hydraulic skeleton and setae cause the body to anchor firmly in the soil.

Thus, the correct answer is option C.