  Generalizing even-like duadic cyclic codes and Type-II duadic negacyclic
codes, we introduce even-like (i.e.,Type-II) and odd-like duadic constacyclic
codes, and study their properties and existence. We show that even-like duadic
constacyclic codes are isometrically orthogonal, and the duals of even-like
duadic constacyclic codes are odd-like duadic constacyclic codes. We exhibit
necessary and sufficient conditions for the existence of even-like duadic
constacyclic codes. A class of even-like duadic constacyclic codes which are
alternant MDS-codes is constructed.
