The main excretory product of earthworm is

Step 1: Analyze the question We need the main nitrogenous excretory product of the earthworm (an annelid). Earthworms excrete through organs called nephridia.

Step 2: Explain the concept Animals excrete nitrogenous waste in three main forms, depending on habitat and water availability:

• Ammonia: very toxic and needs lots of water to flush it out. It is common in aquatic animals such as bony fish.
• Urea: less toxic, moderate water needed. It is common in mammals, amphibians, and earthworms.
• Uric acid: least toxic, needs very little water. It is common in birds, insects, and reptiles.

Step 3: Apply it to the earthworm Earthworms live in moist soil, but they are terrestrial and must conserve some water. Their nephridia excrete mainly urea, along with some ammonia. Studies show that earthworms are ureotelic. They may excrete more ammonia when the soil is very moist, but the standard textbook answer is urea, especially under normal conditions. Carbon dioxide is a respiratory waste, not the main nitrogenous excretory product. Uric acid is characteristic of insects, birds, and reptiles.

Step 4: Answer The correct option is C. urea.

Tip: Remember the pairing: fish → ammonia, earthworm and mammals → urea, insects, birds and reptiles → uric acid. Also remember that earthworms use nephridia, and that is where the urea is removed.