A learner makes a note: a mature earthworm has a swollen glandular band involved in cocoon formation. The missing scientific idea is:

The clitellum is a glandular region in earthworms and some other annelids. It secretes mucus and forms the cocoon during reproduction. This MCQ belongs to the Annelida topic in Animal Diversity-I and is written to test concept understanding rather than memorized wording.