The Peruvian marine invertebrate fauna is thus far poorly investigated referring to sea slugs. From recent surveys along the entire Peruvian coast we present new distributional data on those 15 benthic opisthobranch gastropod species that were formerly known from Chilean waters. Our findings include 12 nudibranch, 1 cephalaspidean and 2 sacoglossan species. These are the first records for Peru of 7 species, such as Janolus rebeccae and Hancockia schoeferti. Known distributional ranges are extended to the north for 9 species, in case of Polycera priva for more than 3000 kilometres; the latter was formerly considered as a Magellanic species endemic to southern Chilean fjords. Photographs of living specimens as well as descriptions of habitats and biological observations are given. We also present the first record of splanchnotrophid copepods from Peru, infesting the aeolid nudibranch Phidiana lottini. Some further data and discussions are provided for species with insufficient or disputed information available.