(a) Prostomium is the frontmost part of the earthworm. This is not called a true segment as it doesn’t contain typical organs of an annelida. The true segment of the earthworm’s body begins from the peristomium.
(b) Septal nephridia are present on both sides of intersegmental septa of earthworm, while pharyngeal nephridia are present in the 4th, 5th and 6th segments. They are same; in terms of structure and function.
