Anterus is a name listed in
Slownik imion, a book published in Poland in 1991 which merely gives lists of the forms of names in 28 different European langauges. It gives Anterus as a name occuring in Polish, Czech, Finnish, and
German, with the original form being Latin Antherus.
Antero is given as the Spanish, Portuguese, and Italian form of the same name.
But I have no idea if Anterus/Antherus is really the name behind Antarius.