Abstract
A new genus of gecarcinucid freshwater crab, Patithelphusa gen. nov., is described from the Shevaroy Hills, Yercaud, located in Salem District, Tamil Nadu, within the Eastern Ghats of India. This new genus is closely related to Baratha Bahir & Yeo, 2007 and Travancoriana Bott, 1969, but can be readily distinguished by a combination of morphological characters, including a relatively broad and shallow cervical groove, triangular bilobed median teeth on the epistomal median lobe, a blunt external orbital tooth with a relatively long outer margin, and a distinct G1 terminal segment terminating in a triangular tip. In addition, morphological characters together with molecular evidence from partial mitochondrial 16S rRNA gene sequences support the recognition of Patithelphusa yercaudensis sp. nov. as a distinct species, exhibiting a genetic divergence of 9.66% from its closest relative, Travancoriana schirnerae Bott, 1969. Phylogenetic analyses based on Bayesian inference and maximum-likelihood approaches recovered the newly described species as a well-supported monophyletic clade, distinctly separated from other known gecarcinucid taxa from India and the geographically proximate region of Sri Lanka. With the addition of this new genus and species, the diversity of Indian gecarcinucid crabs increases to 112 species across 31 genera. Furthermore, biogeographic inferences suggest that the new genus and species may be isolated from its closest gecarcinucid relatives by the wide valleys and the Cauvery River system, which likely act as ecological and geographical barriers. These unique topographical features may restrict gene flow and limit dispersal among high-altitude, habitat-specialist decapods, providing a refuge that facilitates the evolution of novel taxonomic units in peninsular India.