Question

The structure in earthworms which serves as a wedge to force open cracks in the soil is-
(a) Peristomium
(b) Setae
(c) Typhlosole
(d) Prostomium

Answer 1

Hint: It is the anterior-most muscular lobe, hanging out from the mouth of Earthworm. It also helps in sensation.
The prostomium in earthworms seven as a wedge to force open cracks in the soil into which the earthworm may crawl.

Complete answer: The earthworm is a terrestrial invertebrate which belongs to the class Clitellata and phylum Annelida. They are externally segmented with corresponding internal segmentation. Earthworms’ bodies are made up of many ring-like segments called annuli. These segments are covered in setae which the worm uses to move and burrow.
Earthworms depend on prostomium and their sensory receptors to feel their way through the soil. As the earthworm tunnels through the soil, prostomium secretes mucus from its body. It helps them to push into the soil. The prostomium also serves as a sensory device. The earthworms use their prostomium to sense the environment as they do not have eyes, ears, nose, or hands to gather sensory information about their environment.

So, the correct answer is ‘Prostomium’.

Note: The earthworms are also called ‘nightcrawlers’ as they are usually seen feeding above ground at night. They burrow during the day time and are capable of digging down as deep as 6.5 feet. The worm’s first segment called the Periosteum contains their mouth. During burrowing, they consume soil and extract nutrients from decomposing organic matter like leaves and roots.