First record of Onchidium reevesii from Korean tidal flats (Mollusca, Gastropoda, Onchidiidae)

Air-breathing marine slugs of the family Onchidiidae inhabit intertidal environments worldwide, but their diversity and distribution remain poorly documented in Korean tidal flats, particularly in upper intertidal and supralittoral habitats such as saltmarsh vegetation. The following report documents the first confirmed record of Onchidium reevesii from Korea, based on specimens collected from saltmarsh vegetation in the upper intertidal and supralittoral zones of Korean tidal flats at three localities: Jindo, Muan and Suncheon. Species identification was facilitated by an integrative taxonomic approach, incorporating external morphology, radular characters and mitochondrial COI and 16S rRNA sequence analyses. The Korean specimens closely matched the diagnostic morphological features described for Chinese specimens in previous studies. Furthermore, molecular analyses revealed a high degree of sequence similarity, which supports a close phylogenetic affinity with reported sequences of O. reevesii . This record constitutes the first genetic confirmation of O. reevesii on the Korean Peninsula, thereby extending the known geographic distribution of the species across the Yellow Sea in East Asia.