What is "nephridiopore"

n. The external opening of a nephridium

Nephridiopore is part of the nephridia, an excretory organ found in many organisms, such as flatworms or annelids. Polychaetes typically release their gametes into the water column using nephridiopores.

Nephridia are analogous to nephrons or uriniferous tubules found in the kidney of humans.

The nephridia consists of an opening called nephrostome, a long convoluted tubule and another opening called the nephridiopore. Body fluids are filtered in through the nephrostome and passed through the convoluted tubule system. Essential substances are reabsorbed through active mechanisms and waste products are secreted back into the lumen of the tube. The resulting excretory fluid or urine is passed out through the nephridiopore.