What is the function of the clitellum, the only organ visible externally on earthworms?
It anchors earthworms during locomotion.
It pumps blood throughout the body.
It allows earthworms to inhale air.
It secretes mucus that is important in reproduction.
The correct answer and explanation is:
Correct Answer:
It secretes mucus that is important in reproduction.
Explanation:
The clitellum is a specialized, glandular structure found in certain annelids, including earthworms. It is a thickened, saddle-like band that encircles the worm’s body and plays a crucial role in reproduction. The clitellum is typically located closer to the anterior (head) end of the worm and is the only externally visible organ.
During reproduction, the clitellum secretes mucus that serves multiple important functions. First, it helps in copulation by producing a sticky mucus that holds two mating worms together while they exchange sperm. Earthworms are hermaphrodites, meaning each worm has both male and female reproductive organs, but they still require another worm to reproduce.
After mating, the clitellum secretes a thick, mucous sheath that hardens into a cocoon. This cocoon encases the fertilized eggs and provides a protective environment for embryonic development. The clitellum also produces a protein-rich substance that nourishes the developing embryos. Over time, the cocoon is deposited in the soil, where the young worms eventually hatch.
Aside from reproduction, the clitellum also plays a minor role in moisture regulation, helping the worm maintain hydration by secreting mucus. This is important because earthworms breathe through their skin, and a moist environment is necessary for efficient gas exchange.
The presence of a clitellum is also an indicator of sexual maturity in earthworms. Young worms do not have a visible clitellum; it develops as the worm reaches adulthood and becomes capable of reproduction.
In summary, the clitellum is a critical organ in the reproductive cycle of earthworms, facilitating mating, cocoon formation, and embryonic development while also helping maintain moisture levels essential for survival.