Think Before You List: Integrative Systematics of an 'Endemic and Critically Endangered' Butterfly in the Sundarbans

Accurate species delineation is fundamental to understanding evolutionary relationships and guiding effective conservation measures. While the IUCN Red List serves as a critical conservation tool, its reliability hinges on precise systematic species identification and comprehensive distribution data. However, taxonomic inconsistencies remain a major challenge, particularly for poorly studied taxa in complex ecoregions like the Sundarbans mangrove forest. Here, we investigated the taxonomic identity of the Sundarbans Crow, Euploea crameri nicevillei (Moore, 1890), which is considered the only endemic and critically endangered butterfly of Bangladesh, reported only from the Sundarbans mangroves. The taxonomic status of this butterfly has long been debated, with authors regarding it as a morph of Euploea core (Cramer, 1780), while others designated it as a distinct subspecies of E. crameri (Lucas, 1853). Thus, we applied an integrative taxonomic approach incorporating morphological and molecular evidence with field observations and found that the E. crameri nicevillei is conspecific with the E. core. Based on its distinctive external wing morphology and geographic distribution, we recognize it as a valid subspecies of that, E. core nicevillei (Moore, 1890), stat. nov. Furthermore, this subspecies has a wider geographical range than previously assumed. These results suggest that its earlier designation as endemic and critically endangered was premature, emphasizing the importance of rigorous integrative systematics and the need to reassess its conservation status in Bangladesh.