Maniratnam, a Dalit leader and Congress functionary of Chidambaram, joined PMK a few days ago after he was denied ticket to contest the seat.
Congress has nominated P Vallalperumal as its candidate and the PMK had named C Gopalakrishnan for Chidambaram, who has now been replaced.
A PMK release here also announced Vadivel Ravanan as its nominee for the Nagapattinam constituency.