nephridium
A nephridium (plural nephridia) is a tubular excretory organ found in many invertebrates. It functions in removing metabolic wastes and in regulating water balance and ion concentrations, often integrating excretion with osmoregulation.
There are two main categories of nephridia. Protonephridia are closed tubules that end blindly with a flame
Metanephridia are typically found in segmented animals such as annelids. In these, each body segment usually
In earthworms, the extensive system of metanephridia per segment illustrates how these organs support large-scale osmoregulation