Hi, I do not know if the Jan Nepomucen Lukaszewicz line is actually related to me. This was told to me by a Lukoseviicus family member in Lithuania.
In the Lithuanian surname dictionary, Mordas comes from these towns
MOR̃DAS Žg; MORDAS Dt, Kdn, Kn 3 (6). lš Mórdasas (žr.) ar pan.
Dt Dotnuvà (Kėdáinių r.)
Kdn Kėdáiniai
Kn Kaũnas
Žagãrė (Jõniškio r.)
As you can see it is not common