Flame cells are characteristic of the excretory system of which phylum?

• A. Platyhelminthes
• B. Nematoda
• C. Annelida
• D. Cnidaria

Answer: (A)

Flame cells are part of a protonephridial excretory system that flatworms use to regulate water balance and remove wastes. In these organisms, a network of tubules begins with flame cells—ciliated units that beat like a tiny flame to draw in fluids from the body cavity. The filtrate then travels through tubules and out through excretory pores, helping both excretion and osmoregulation in animals with no true body cavity. This setup is characteristic of the flatworm phylum, Platyhelminthes.

In other phyla, excretion works differently: nematodes use a simple excretory system without flame cells, annelids have metanephridia with nephrostomes, and cnidarians lack a true excretory system altogether.