Abstract
This study reports the discovery of four new benthic harpacticoids from Korean waters in the Pacific Ocean. The harpacticoids were collected using SCUBA or a grab sampler and sorted using a stereomicroscope for both molecular and morphological analysis. The study employed standard DNA sequencing methods (COI and 18S rRNA) and detailed morphological characterization through microscopy and scanning electron microscopy. As a result, three new species belonging to the family Orthopsyllidae and classified as a new genus were discovered. Although the new genus lacks brush setae on leg 1, a diagnostic feature of Orthopsyllidae, it shares similarities with other orthopsyllids in characters such as the large thorn-like process on the antennule, leg 5, and sexual dimorphism. This finding necessitates an expanded diagnosis of Orthopsyllidae to reflect the characters of the new genus based on the three new species. In addition, a new species belonging to the genus Orthopsyllus was discovered. This study is the first to describe a new species of Orthopsyllus from Korea, where the genus has not been previously reported at the species level. This study provides a key for classifying genera and species within the Orthopsyllidae family.