The external segments are usually definable by the setae; and if the setae are absent, as in the anterior segments a, Penial seta of Perichaeta ceylonica.
सीमांकनका बारेमा त्यतिबेलै निर्णय भएकै हो तर अहिले आएर उहाँहरु फेरि आयोग बनाउने कुरा गर्दै हुनुहुन्छ ।