Resumen
Two marine halacarids, Copidognathus levicostatus n. sp. and C. vicinus Bartsch, 1997, belonging to the C. gibbus group, have been recorded based on both sexes from the microhabitat of intertidal and sublittoral rocks on the coast of South Korea. Copidognathus levicostatus n. sp. Is characterized by a combination of features, as follows: the absence of areolae with rosette pores on all dorsal and ventral plates, the presence of a short frontal process, a pair of costae with raised narrow ribs on the posterior dorsal plate, the partial fusion of the anterior epimeral plate and genitoanal plate in both sexes, and three pairs of perigenital setae in the male. The Korean specimens of C. vicinus Bartsch, 1997 agree well with the original description from Hong Kong, except for the lateral claws bearing a comb. This study provides detailed (re)descriptions of the morphological characteristics of the two Korean halacarid species, C. levicostatus n. sp. and C. vicinus, based on illustrations and scanning electron microscope photomicrographs. Additionally, we present a dichotomous key for known Copidognathus species in Korean waters, accompanied by a brief comment on their occurrence in various microhabitats, especially their habitat preferences for geniculate and non-geniculate red coralline algae.