metanephridium

A type of excretory gland or nephridium found in many types of invertebrates such as Annelids, Arthropods and Molluscs. It typically consists of a ciliated funnel opening into the body cavity or coelom connected to a duct which may be variously glandularized, folded or expanded (vesiculate) and which typically opens to the organism's exterior. These ciliated tubules pump water carrying surplus ions, metabolic waste, toxins from food, and useless hormones out of the organism through openings known as nephrostomes. This waste is passed out of the body at the nephridiopore. The primary urine produced by filtration of blood (or a similar functioning fluid) is modified into secondary urine through selective reabsorption by the cells lining the metanephridium. In many earthworms the nephridial ducts open into the digestive tract instead, a condition known as enteronephry.