Ischyodus was rather similar to the present-day chimaera Chimaera monstrosa, which is found in the Atlantic Ocean and Mediterranean Sea.
In the holocephalan species Chimaera monstrosa (ratfish), he described, in the basal midline of the diencephalon, a previously unknown ependymal structure adjacent to the rostral part of the optic chiasma referred to as the ‘organon vasculare praeopticum’.