Flatworm anatomy

The nephridium (: nephridia) is an invertebrate organ, found in pairs and performing a function similar to the vertebrate kidneys (which originated from the chordate nephridia). Nephridia remove metabolic wastes from an animal's body and come in two basic categories: metanephridia and protonephridia. In some cases, nephridia may fuse or become functionally integrated with coelomoducts—mesodermal structures that open from the coelom to the exterior—to form a more complex structure known as a nephromixium. All animals possessing nephridia or kidneys belong to the clade Nephrozoa.

specialised attachment organ of an animal

gland of reproductive system in Platyhelminthes