This dataset comprises occurrence records on sea slugs, collected from divers worldwide via the online platform "Sekai no Umiushi" (https://seaslug.world/) since 2015. Data collection remains ongoing, and the dataset currently includes approximately 40,000 records. It broadly covers groups within the Heterobranchia commonly known as "sea slugs," including not only nudibranchs (Nudibranchia) but also sea hares (Aplysiida), headshield slugs (Cephalaspidea), and sap-sucking slugs (Sacoglossa). The key feature of this dataset is that every record is accompanied by a high-resolution photograph that serves as the basis for identification. All species identifications are consistently performed by the project administrator based on these photographs, ensuring high taxonomic accuracy and consistency throughout the entire dataset. Each record includes a scientific name, vernacular name, geographic coordinates, event date, depth, and a URL to the photograph. This dataset, underpinned by photographic evidence, provides valuable contributions to studies on sea slug biogeography, understanding of diversity patterns, and marine biodiversity monitoring research through citizen science.