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 option is (a), (b) and (c) are correct.

Let us analyze each of the statements to understand the structure and functions of the prostomium in an earthworm:

Statement (a): It serves as a covering for mouth.
The prostomium is a small, fleshy lobe that projects forward from the front end of the earthworm. It hangs directly over the mouth opening, effectively serving as a protective covering for the mouth. Therefore, statement (a) is correct.

Statement (b): It helps to open cracks in the soil into which it can crawl.
As the earthworm moves through the soil, it uses the prostomium as a wedge to push, loosen, and force open tiny cracks and crevices, which allows the worm to crawl into and navigate through the dirt. Therefore, statement (b) is correct.

Statement (c): It is one of the sensory structures.
The prostomium contains numerous sensory cells (chemoreceptors and tactile receptors) that help the earthworm sense its surrounding environment, detect chemicals, and perceive touch. Therefore, statement (c) is correct.

Statement (d): It is the first body segment.
In earthworms, the first true body segment is called the peristomium (or buccal segment), which surrounds the mouth. The prostomium is a pre-segmental lobe that sits in front of the peristomium rather than being a true segment itself. Therefore, statement (d) is incorrect.

Since statements (a), (b), and (c) are correct, and statement (d) is incorrect, the correct combination is (a), (b) and (c) are correct.