The clitellum is a specialized, glandular section of the body in certain annelids, such as earthworms and leeches. It is typically a prominent, swollen band that plays a crucial role in reproduction, producing a mucus secretion that forms a cocoon for fertilized eggs. The clitellum is most noticeable during the breeding season when it becomes more pronounced. Its primary function is to aid in the development and protection of offspring.