Question

Earthworms have no skeleton, but during burrowing, the anterior end becomes turgid and acts as a hydraulic skeleton. This is due to
A. Setae
B. Gut peristalsis
C. Blood
D. Coelomic fluid

Answer 1

Hint: Movement in earthworms is due to two structures- setae and muscles of the body. Setae helps for anchoring the body in a particular place, the muscles help in the forward and backward movement from that place. For the movement of the worm the longitudinal and circular muscles of the body work in unison.
Complete step-by-step answer: Earthworms are made up of 100 to 150 round segments. Each segment contains muscles, blood vessels, nerves and internal organs. These muscles are of two types- Longitudinal muscles and circular muscles. Longitudinal muscles run through the length of the earthworm and circular muscles are perpendicular to the longitudinal muscles and surround the worm from all the sides.
Earthworms have a special type of skeleton known as hydrostatic skeleton. This means that earthworms have their bodies filled with fluid unlike other true skeletons. This fluid provides the necessary shape to the worm’s body, even under the pressure exerted by the soil.
The hydrostatic skeleton of the earthworm is filled with coelomic fluid. This fluid helps in the locomotion of the earthworm. When the circular muscles contract the coelomic fluid makes those regions stiff and the longitudinal muscles relax. When the circular muscles relax the longitudinal muscles contract and this way the entire body of the earthworms moves ahead making a burrow in the soil.
Therefore, the correct answer is option D- Coelomic fluid.
Note: Coelomic fluid in the hydraulic skeleton is responsible for movement of the earthworm. The coelomic fluid generally makes the region stiff which is located just behind the anterior region,due to this, the anterior region of the earthworm gets turgid and acts as a hydraulic skeleton.This is done so that the muscles are able to push the entire body in the forward direction.