Respiratory and Excretory System of Earthworm

Respiratory System

Earthworm respires, but has no respiratory organs, exchange of gases takes place through moist skin. Surface area of earthworm is more than its volume, so earthworm does not require

any respiratory organ.

Excretory System

Excretory organs of earthworm are segmental nephridia, ectodermal in origin, analogous to vertebrate kidney.

Fig. Various types of nephridia and their Fig. A septal nehridium of Pheretima
arrangement in Pheretima

Three main types of nephridia are :

Pharyngeal nephridia,

Integumentary nephridia,

Septal nephridia.

Pharyngeal nephridia : are situated in the segments 4, 5 and 6. They open in the anterior part of alimentary canal, i.e., buccal cavity and pharynx. They are without nephrostome and are enteronephric type.

Integumentary nephridia are scattered in the body wall. They are smallest, V-shaped without nephrostome and are exonephric type (200 - 250 in each segment). In clitellum there are 2000 nephridia.

Septal nephridia are the largest, attached to both faces of each intersegmental septum behind 15th segment.

Each intersegmental septum bears two rows of septal nephridia numbering 80 – 100 on each septum. They are absent in anterior 14 segments.

Septal nephridia are the only nephridia with nephrostome or funnel. These canals open in turn into two supra-intestinal excretory canals. They are enteronephric and excretory products

are finally poured into intestine.

Enteronephric condition is an adaptation for the conservation of water.

The nephridia extract water and excretory substances from both blood and coelomic fluid by ultrafiltration.

Excretory products of earthworm are urea (about 40%), ammonia (about 20%) and traces of creatinine, amino acids (40%). No uric acid.

Earthworms are mainly ureotelic.