Anthelmintically active compounds of formula I are described ##STR1## in which R.sub.1 is hydrogen, halogen, C.sub.1 -C.sub.2 alkyl, C.sub.1 -C.sub.2 thioalkyl, C.sub.1 -C.sub.2 haloalkyl, nitro, C.sub.1 -C.sub.2 alkoxy, or the group SO.sub.n R in which R is C.sub.1 -C.sub.2 alkyl or phenyl and n is 0, 1 or 2;R.sub.2 is hydrogen, halogen, C.sub.1 -C.sub.2 alkyl, C.sub.1 -C.sub.2 haloalkyl, C.sub.1 -C.sub.2 haloalkoxy or C.sub.1 -C.sub.2 alkoxy;R.sub.3 is hydrogen or C.sub.1 -C.sub.2 alkyl;R.sub.4 is hydrogen or C.sub.1 -C.sub.2 alkyl;R.sub.5 is hydrogen, halogen or C.sub.1 -C.sub.5 alkyl;R.sub.6 is hydrogen, halogen or C.sub.1 -C.sub.5 alkyl;R.sub.7 is hydrogen, halogen, C.sub.1 -C.sub.2 alkyl, nitro, C.sub.1 -C.sub.2 haloalkyl, C.sub.1 -C.sub.2 haloalkoxy or C.sub.1 -C.sub.2 alkoxy;R.sub.8 is hydrogen, halogen, C.sub.1 -C.sub.2 alkyl, C.sub.1 -C.sub.2 haloalkyl, C.sub.1 -C.sub.2 haloalkoxy or C.sub.1 -C.sub.2 alkoxy;R.sub.9 is hydrogen, halogen, C.sub.1 -C.sub.2 alkyl, C.sub.1 -C.sub.2 haloalkyl, C.sub.1 -C.sub.2 haloalkoxy or C.sub.1 -C.sub.2 alkoxy;R.sub.10 is hydrogen, halogen, C.sub.1 -C.sub.6 alkyl, C.sub.1 -C.sub.2 haloalkyl, C.sub.1 -C.sub.2 alkylthio, C.sub.3 -C.sub.6 cycloalkyl or cyano;R.sub.11 is hydrogen, halogen, C.sub.1 -C.sub.6 alkyl, C.sub.1 -C.sub.2 haloalkyl, C.sub.1 -C.sub.2 alkylthio or C.sub.3 -C.sub.6 cycloalkyl;R.sub.12 is hydrogen or halogen; and Y is .dbd.CH-- or .dbd.N-; including the physiologically tolerable acid additon salts thereof, and also the preparatin and use thereof and novel intermediates.