Excretory System of Earthworm
Excretion is a process through which metabolic waste is eliminated from the body of the
animal. Earthworms are both ammonotelic and ureotelie. The main excretory organs in
earthworm are nephridia (sing, nephridium) which perform the function of excretion and
osmoregulation. These are generally unbranched and open into coelom by a ciliated funnel
called nephrostome. These types of ciliated funnel shaped nephridia are called.
Metanephridium. But some cases branched nephridia can also be seen. Nephridia are
ectodermal in origin.
The nephridia occur in all the segments of earthworm except in the first three segments.
Three types of nephridia are found in the earthworm according to their location, namely
the Septal nephridia, Pharyngeal nephridia, and integumentary nephridia.
Septal nephridia:
They are present attached to the septa behind the fifteenth segment. Each septum bears
about 40-50 septal nephridia attached to its anterior and posterior surfaces. Thus there are
80 to 100 septal nephridia in each segment.
Since the septal nephridia discharge their excretory matter into the lumen of the alimentary
canal/enteron, they are called enteronephric nephridia. The opening of the nephridia into
the alimentary canal is an adaptation for the conservation of water which is absorbed by
the internal epithelial lining of intestine.
Pharyngeal nephridia:
They occur in three pairs of tufts in the 4th, 5th, and 6th segments lying on each side of the
pharynx and oesophagus. Each tuft consists of hundreds of nephridia without
nephrostome. There are three pairs of common pharyngeal nephridial duets which run
anteriorly parallel to the ventral nerve cord. The ducts of the nephridia of the sixth segment
open into the buccal cavity while the ducts from the nephridial bunches of the fourth and
fifth segments open into the pharynx. These nephridia are also enteronephric.
These ducts carry excretory matter from the pharyngeal nephridia into the gut (buccal
cavity/pharynx). Thus like septal nephridia, the pharyngeal nephridia are also enteronephric
nephridia. Enteronephric condition is an adaptation for the conservation of water which is
absorbed by the inner lining of the alimentary canal.
Integumentary nephridia:
They are found scattered in the body wall (integument) in each segment except the first
two segments. In each segment they number from 200 to 250 except in the 14 th to 16th
segments (clitellar region) where their number is about ten times more than that in the
other segments. Thus clitellar segments are often called as the “forest of nephridia”. They
are the smallest of the three types of nephridia and V-like in shape which lack
nephrostomes. These nephridia discharge their contents directly to the outside hence they
Excretion is a process through which metabolic waste is eliminated from the body of the
animal. Earthworms are both ammonotelic and ureotelie. The main excretory organs in
earthworm are nephridia (sing, nephridium) which perform the function of excretion and
osmoregulation. These are generally unbranched and open into coelom by a ciliated funnel
called nephrostome. These types of ciliated funnel shaped nephridia are called.
Metanephridium. But some cases branched nephridia can also be seen. Nephridia are
ectodermal in origin.
The nephridia occur in all the segments of earthworm except in the first three segments.
Three types of nephridia are found in the earthworm according to their location, namely
the Septal nephridia, Pharyngeal nephridia, and integumentary nephridia.
Septal nephridia:
They are present attached to the septa behind the fifteenth segment. Each septum bears
about 40-50 septal nephridia attached to its anterior and posterior surfaces. Thus there are
80 to 100 septal nephridia in each segment.
Since the septal nephridia discharge their excretory matter into the lumen of the alimentary
canal/enteron, they are called enteronephric nephridia. The opening of the nephridia into
the alimentary canal is an adaptation for the conservation of water which is absorbed by
the internal epithelial lining of intestine.
Pharyngeal nephridia:
They occur in three pairs of tufts in the 4th, 5th, and 6th segments lying on each side of the
pharynx and oesophagus. Each tuft consists of hundreds of nephridia without
nephrostome. There are three pairs of common pharyngeal nephridial duets which run
anteriorly parallel to the ventral nerve cord. The ducts of the nephridia of the sixth segment
open into the buccal cavity while the ducts from the nephridial bunches of the fourth and
fifth segments open into the pharynx. These nephridia are also enteronephric.
These ducts carry excretory matter from the pharyngeal nephridia into the gut (buccal
cavity/pharynx). Thus like septal nephridia, the pharyngeal nephridia are also enteronephric
nephridia. Enteronephric condition is an adaptation for the conservation of water which is
absorbed by the inner lining of the alimentary canal.
Integumentary nephridia:
They are found scattered in the body wall (integument) in each segment except the first
two segments. In each segment they number from 200 to 250 except in the 14 th to 16th
segments (clitellar region) where their number is about ten times more than that in the
other segments. Thus clitellar segments are often called as the “forest of nephridia”. They
are the smallest of the three types of nephridia and V-like in shape which lack
nephrostomes. These nephridia discharge their contents directly to the outside hence they
