Question

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

Hint: The earthworm belongs to phylum Annelida. They have soft bodies and lack true skeletons. Earthworms possess hydrostatic skeletons with soft muscles which provide flexibility to the organism.

Complete answer:
 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 backwards. The locomotion is brought about by the increase in the hydrostatic pressure of the interior ten segments. There is a contraction of the circular muscles which begins at the interior and the wave passes backwards. This causes the anterior region to extend.

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 and which shortens the anterior Indian causes the posterior part of the body to pull forward. These moments of contraction and relaxation result in the locomotory movement. The coelomic fluid serves as a hydraulic skeleton and seat causes the body to anchor firmly in the soil.
Blood- The blood contains respiratory pigment which helps in transport of respiratory gases.
Alimentary canal laden with mud- It is the part of the digestive system.
Ventral nerve cord- It is the major structure of the nervous system. It controls the neural signals to and fro from the brain and body.

Thus, the correct answer is option “C”.

Note: The advantages of hydrostatic skeleton are:
i) The fluid helps them to move easily during swimming and burrowing.
ii) Help them from protecting themselves from predators.
iii) The lightweight and flexible skeleton helps them to move anywhere with little muscle mass.
iv) The healing capacity of the organism is more as compared to that of a hard skeleton.