Practice question

Amphioxus renal system consists of approximately 90 pairs of segmental protonephridia located above pharynx, each tubule bears clusters of solenocytes, specialized cells with long flagellum inside a microvillar collar creating filtration current, analogous to annelid flame cells but with distinct ultrastructure. Filtrate from coelom and blood plexus passes into atrium, then expelled via atriopore. No Malpighian tubules which are insect terrestrial organs, nor metanephridia of annelids or vertebrate kidneys occur. Presence of solenocyte protonephridia evidences primitive excretory arrangement bridging invertebrate protonephridial systems and vertebrate nephric evolution within deuterostomes.