Reeves’ Turtles (also known as Chinese Three-Keeled Pond Turtles, Mauremys reevesii) exhibit temperature-dependent sex determination (TSD). Recent studies reported genome sequencing and described normal embryonic and gonadal developmental patterns in M. reevesii, making them a promising model for studying TSD. Nevertheless, development of other reproductive organs, such as the Müllerian duct, has not been described in this species. The Müllerian duct is a tubular structure that primarily forms in mesonephros during embryogenesis in both sexes. While the Müllerian duct further develops into the reproductive tract in females, it typically regresses in males. In this study, we investigated the development and regression of the Müllerian duct in M. reevesii during the latter half of embryogenesis under female- (FPT; 31°C) and male-producing temperatures (MPT; 26°C). Histological analysis revealed that the Müllerian duct showed the first sign of regression at the end of the temperature-sensitive period under MPT and significantly regressed at the prehatching stage (stage 24). Development and regression of the Müllerian duct in M. reevesii followed general trajectories reported in mouse and chicken studies. Timing of regression was consistent with reports in another TSD turtle, Pond Sliders (Trachemys scripta). Our study provides a basis for comparative studies of reproductive organs in TSD species and for elucidating mechanisms leading to sexual differentiation.

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