The nephridia may be of two types as micronephridia and metanephridia. Micronephridia is smaller in size, sometimes microscopic and are numerous in each segment. All the nephridia of Pheretima are microscopic micronephridia. Meganephridia is larger in size and present from clitellar region to the end. There are 200-250 of these exonephric metanephridia per segment. So, the correct answer is option D.