Question

Differentiate protonephridia from metanephridia.

Answer 1

Two different kinds of nephridia occur within the Bilateria, protonephridia closed up by a terminal cell and metanephridia opening into the coelomic cavity. Both initially filter and subsequently modify intercellular fluids. Whereas metanephridia are strictly correlated to a coelom, proto-nephridia occur in acoelomate as well as in coelomate organisms. Protonephridia of different bilaterian taxa correspond to each other in several structural features.