Following are the statements about prostomium of earthworm.

(a) It serves as a covering for mouth.

(b) It helps to open cracks in the soil into which it can crawl.

(c) It is one of the sensory structures.

(d) It is the first body segment.

Choose the correct answer from the options given below.

The correct answer is (a), (b) and (c) are correct.

Let us analyze each of the given statements regarding the prostomium of an earthworm step-by-step:

Statement (a): It serves as a covering for mouth.
This statement is correct. The prostomium is a lobe that overhangs the mouth of the earthworm, acting as a protective wedge or covering for the mouth opening.

Statement (b): It helps to open cracks in the soil into which it can crawl.
This statement is correct. The prostomium is muscular and serves as a wedge to force open narrow cracks and crevices in the soil, allowing the earthworm to burrow and crawl through.

Statement (c): It is one of the sensory structures.
This statement is correct. The prostomium contains sensory receptors that help the earthworm sense light, touch, and chemical stimuli in its environment.

Statement (d): It is the first body segment.
This statement is incorrect. The prostomium is not a true body segment; rather, it is a pre-oral lobe situated in front of the mouth. The actual first body segment of an earthworm is the peristomium (or buccal segment), which contains the mouth.

Therefore, statements (a), (b), and (c) are correct, while statement (d) is incorrect.