Nephridia are simple or branching tubules used for excretion which open to the exterior through pores called nephridiopores.
Two major types of nephridia are as follows:
i. Protonephridia:
These are network of dead end tubes called flame cells. They are mostly found in animals that lack a true body cavity, e.g. Platyhelminthes, rotifers, some annelids and Amphioxus.
ii. Metanephridia:
These are unbranched coiled tubes that are connected to the body cavity through funnel like structures called nephrostomes. Body fluid enters the nephridium through nephrostome and gets discharged ‘ through nephridiopore. e.g. Earthworms.
