Normal Embryonic Stages of the Chinese Softshelled Turtle Pelodiscus sinensis (Trionychidae)

We describe the normal embryonic development of the Chinese soft-shelled turtle, Pelodiscus sinensis. We identified 23 stages between the late neurula and hatching, based on chronology and the external morphology of embryos. The anlage of the sensory organs appeared in early stages of the pharyngula, followed by limb buds. The lateral ridge of the carapace, or the carapacial ridge, could be recognized by two weeks of incubation, and the basal structure of the shell was complete by the mid stage (24 days) of development. The hatchling was well pigmented, and the yolk had been entirely absorbed. The developmental stages of P. sinensis were comparable with those of other turtle species. The developmental pattern of P. sinensis resembled basal taxa rather than more derived groups. Some peculiarities were recognized in the development of P. sinensis, including the appearance of cutaneous papillae on the carapace instead of horny scutes. Those features are shared by Carettochelys, possibly the species taxonomically closest to the Trionychids.