Reproduction in earthworm - SS2 Biology Lesson Note

Earthworms, belonging to the phylum Annelida, exhibit a unique type of reproduction called hermaphroditic reproduction, specifically known as simultaneous hermaphroditism. This means that each individual earthworm possesses both male and female reproductive organs, allowing them to produce both sperm and eggs. Here's an overview of the reproductive process in earthworms:

1.       Mating: Earthworms engage in mating behavior to exchange sperm with another individual. Mating typically occurs on the surface of the soil during favorable environmental conditions, often after rainfall. Earthworms come to the surface and align themselves in opposite directions, binding their anterior ends together.

2.       Exchange of Sperm: Once in this position, the earthworms align their clitella, which are swollen and lighter-colored segments located near the anterior ends of their bodies. The clitella secrete a mucus cocoon that slides over the worm's body, picking up sperm from the seminal receptacles (sperm storage structures) in each worm. The sperm is exchanged between the two earthworms, allowing both individuals to acquire genetic material from each other.

3.       Cocoon Formation: After the sperm exchange, the earthworms separate, and each secretes its own mucus ring or cocoon, which contains both the eggs and sperm. The cocoon is deposited in the soil near the burrow or in a protective underground chamber.

4.       Development: Fertilization occurs within the cocoon as the eggs become fertilized by the stored sperm. The cocoon provides a protective environment for the developing embryos. Over a period of a few weeks, the young earthworms develop inside the cocoon.

5.       Hatching and Growth: When the embryos inside the cocoon mature, they hatch as miniature versions of adult earthworms. The juvenile earthworms emerge from the cocoon and start growing. They will continue to grow and develop through a series of molts, shedding their outer layer or cuticle.

It is important to note that earthworms can also undergo asexual reproduction by fragmentation. If a part of an earthworm's body becomes separated from the rest, it can regenerate into a complete individual. However, sexual reproduction through mating is the primary method of reproduction in earthworms.

Overall, the hermaphroditic nature of earthworms allows them to engage in cross-fertilization, ensuring genetic diversity within the population.