Metanephridium (pl. metanephridia) is a type of excretory gland or nephridium found in many types of invertebrates such as annelids and mollusks. 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. In many earthworms these nephridial ducts open into the digestive tract instead.
Metanephridium (pl. metanephridia) is a type of excretory gland or nephridium found in many types of invertebrates such as arthropods and mollusks.
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.
The primary urine produced by filtration of blood (or a similar functioning component) are modified into secondary urine through selective reabsorption by the cells lining the metanephridium.
One thing that a metanephridium can do that protonephridia cannot is to sweep small particulate materials, such as bacteria, into their funnel, and thence eventually out of their body.
A diagram of a metanephridium of an earthworm (modified from Kozloff, 1990).
Although the description of the metanephridium is relatively simple, the physiological reactions occurring in it are anything but simple.
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