The excretory organs of earthworms are known as:

The correct option is Nephridia.

Explanation

Excretion involves the elimination of metabolic waste products from the body. Different animal phyla have evolved specific specialized structures for excretion and osmoregulation depending on their complexity and habitat.

Detailed Analysis:

• Nephridia is Correct: Nephridia are the excretory organs of earthworms and other members of the Phylum Annelida. They are coiled tubular structures that help remove nitrogenous wastes and maintain fluid and ionic balance.
• Flame cells is Incorrect: Flame cells (or protonephridia) are the specialized excretory structures found in Platyhelminthes (Flatworms), such as Planaria.
• Green glands is Incorrect: Green glands (also known as antennal glands) are the excretory organs found in certain crustaceans (Phylum Arthropoda), such as prawns.
• Kidneys is Incorrect: Kidneys are the complex excretory organs found in Vertebrates, responsible for filtering blood and producing urine.

Key Takeaway:
The excretory structures in the animal kingdom are phylum-specific: Nephridia for Annelids (Earthworms), Flame cells for Flatworms, Malpighian tubules for Insects, and Green glands for Crustaceans.