What is the function of nephridia in an earthworm?

Nephridia are the earthworm’s excretory organs that remove body wastes and keep the body’s water and salt balance right. Nephridia act like tiny kidneys in earthworms. They collect liquid wastes from body fluid (coelomic fluid and blood), filter them, and throw them out through small pores to the outside. By doing this, nephridia keep the worm’s internal environment clean and stable, which is called excretion and osmoregulation.

Key roles of nephridia (excretion and balance)

• Remove nitrogenous wastes: mainly ammonia and urea formed from protein breakdown.
• Regulate water and salts: control the amount of water and ions (like sodium, potassium, chloride) to prevent swelling or drying.
• Maintain internal pH and ionic balance: keeps the internal fluid suitable for enzyme action and life processes.
• Help in homeostasis: steady internal conditions despite changes in the soil environment.

Types of nephridia in earthworm (with locations)

How a typical nephridium works (simple flow)

1. Collection: body fluid enters the nephrostome (a ciliated funnel) or via capillaries.
2. Filtration & selective reabsorption: useful water and salts are reabsorbed along the tubule.
3. Formation of urine: remaining fluid becomes dilute urine containing wastes.
4. Elimination: urine leaves through a nephridiopore to the outside or into the gut.