Alpioniscus (Illyrionethes) is a widespread subgenus of Trichoniscidae in the Dinaric Karst with 15 nominal troglobiotic species. Here we redescribe Alpioniscus (Illyrionethes) magnus and describe three new species (A. lossinii n. sp., A. drazinai n. sp., and A. mandalinae n. sp.) restricted to coastal areas. As a result, 18 nominal Illyrionethes species are known from the Dinaric Karst.
Keywords: Adriatic coast, cave fauna, new species, terrestrial isopods, troglobionts, Trichoniscinae, Crustacea.