Nephridiopore

A nephridiopore is a pore at the end of the nephridium, an excretory organ found in invertebrates, such as flatworms and annelids. ^[1] Nephridiopores open on the ventral surface of the body wall and allow metabolic wastes filtered by the nephridium to exit the body.^[2]

Nephridia are homologous to nephrons or uriniferous tubules found in the kidneys of vertebrates. They occur in two forms: metanephridia, which begin with a nephrostome, and protonephridia, which begin with a flame cell. Fluids collected by the nephrostome or flame cell pass through a ciliated tubule,^[3] where essential substances are reabsorbed through active mechanisms and waste products are secreted back into the lumen of the tube.^[4] The resulting excretory fluid or urine is then passed out through the nephridiopore.^[3]