Nephridia of Worms
As pointed out earlier, nephridia are the excretory tubules in many invertebrates. While all nephridia open to the exterior by an excretory pore known as nephridiopore, some have their internal end closed and others open internally into the body cavity by a ciliated funnel called nephridiostome. The former type of nephridia is known as protonephridia and the latter type are the metanephridia.