New record of intersex Chinese mitten crab, Eriocheir sinensis (Malacostraca, Decapoda, Varunidae), with typical female appearance and male gonopods, from Nanjing, eastern China

A novel intersex individual of the Chinese mitten crab, Eriocheir sinensis Milne-Edwards, 1853, sampled from Nanjing, eastern China was described herein. The specimen exhibited a fully typical female external phenotype. Its abdomen retained the characteristic circular shape unique to normal females, and the ratios of all measured morphological traits were consistent with the national standards of China for female E. sinensis individuals. A pair of female gonopores was present on the fifth thoracic somite, with the second to fifth pairs of ovigerous pleopods bearing normal setae. Notably, male first gonopods (G1) were observed in this individual, whereas the second gonopods (G2) and penis were absent. Potential hormonal or environmental causes (e.g., IAG/CFSH imbalance, EDCs) underlying this sexual aberration were further discussed. The findings of this study enrich the biological data on intersex phenomena in crustaceans and provide a fundamental reference for exploring the sex differentiation mechanism and environmental adaptation of E. sinensis under habitat disturbance.