Why nephridia in earthworm that are basically similar in structure classified into three types ? Mention the names of each .

Explanation

Though nephridia of earthworm are similar in their basic structure but are classified into three types on the basis of their position:
(i) Pharyngeal nephridia occur in 3 pairs of groups, one pair in each of 4th, 5th and 6th segment of body.
(ii) Integumentary nephridia attached on inner surface of skin in all segments except first two, clitellar and last segments of body.
(iii) Septal nephridia attached on both the sides of intersegmental septa from 15th to last segment of body.