In the Galápagos Islands, research on the distribution of marine invertebrates is constrained by the limited availability of specimen-based data and reliable observations. In this study, we used citizen science to identify new localities for Tyrannodoris leonis (Nudibranchia, Polyceridae), a colorful sea slug species found in the Galápagos Marine Reserve (GMR). We circulated a digital flyer to encourage local and international divers to share their sightings of the species. Additionally, we reviewed records available on the iNaturalist platform from 2018 to 2024. As a result, we obtained 19 new records of T. leonis and updated its distribution map in the GMR with eight newly documented localities. This study highlights the value of citizen science as a complementary tool to museum-based research, contributing to a better understanding of species distribution in marine ecosystems.