Integrative taxonomy reveals a new species of Pachycheles Stimpson, 1858 (Decapoda: anomura: Porcellanidae) from the coral reefs of the South China Sea

Historically, Pachycheles sculptus was considered a widely distributed species in Chinese waters with significant morphological plasticity. In this study, we describe a new species, Pachycheles nanhaiensis sp. nov. discovered in the coral reefs of the Xisha Islands, South China Sea. Based on an integrative taxonomic approach combining morphological examination and molecular analyses (COI, 16S, and Cytb), our results demonstrate that the Xisha population constitutes a distinct evolutionary lineage. Pachycheles nanhaiensis sp. nov. can be distinguished from its most similar congener P. sculptus by the straight and oblique anterior margin of the carpus proximal tooth (distinctly angled in P. sculptus), fewer setae on the ambulatory legs, and a non-anteriorly produced lobe on the cheliped merus. Molecular species delimitation consistently supports the validity of the new taxon. Currently, the new species appears to be restricted to the oceanic coral reefs of the Xisha Islands, while P. sculptus sensu stricto inhabits the mainland coastal waters.