Which excretory system is characteristic of Platyhelminthes?

• A. Protonephridia (flame cells)
• B. Nephridia
• C. Malpighian tubules
• D. Kidneys

Answer: (A)

Platyhelminthes rely on a simple excretory and osmoregulatory system called protonephridia, which use flame cells. These flame cells have cilia that beat to draw body fluids into tiny tubules. As fluid moves through the tubules, valuable water and solutes can be reabsorbed, while wastes and excess water are expelled through excretory pores to the outside. This basic network suits flatworms, which lack a true circulatory or specialized urinary organ, and it handles both waste removal and maintaining water balance through diffusion and selective reabsorption. In other animal groups, different excretory structures are used—nephridia in many annelids, Malpighian tubules in insects, and kidneys in vertebrates—so protonephridia with flame cells are the distinctive excretory feature of Platyhelminthes.