The excretory organ of earthworms is known as

Step 1: Analyze the question The question asks for the excretory organ of the earthworm, which is an annelid (phylum Annelida).

Step 2: Explain the concept Different animal groups have different excretory structures:

• Contractile vacuole: protozoans such as Amoeba and Paramecium. It removes excess water (osmoregulation).
• Flame cells: flatworms such as planaria and tapeworms.
• Malpighian tubules: insects such as cockroaches and grasshoppers.
• Nephridia: annelids such as earthworms.
• Kidneys: vertebrates, including fish, amphibians, reptiles, birds and mammals.

Step 3: Apply it to the earthworm The earthworm's body is divided into segments. Almost every segment has a pair of coiled tubular structures called nephridia (singular: nephridium). Each one collects waste from the coelomic fluid through a funnel-shaped opening called the nephrostome. The waste, mostly ammonia and urea in dilute urine, passes along the tubule and leaves the body through a small pore (the nephridiopore) on the body surface.

Step 4: Eliminate the wrong options

• A: found in single-celled organisms, not earthworms.
• B: found in flatworms.
• C: found in insects and other arthropods.
• E: found in vertebrates. The earthworm is an invertebrate.

Answer: D. nephridium

Tip: Match each animal with its organ using this short list:

• Protozoa → contractile vacuole
• Flatworms → flame cells
• Earthworms (annelids) → nephridia (think "Nephridia for Night crawlers")
• Insects → Malpighian tubules
• Vertebrates → kidneys

NECO and WASSCE often test this matching, so it is worth memorizing.