Intrauterine and post-ovipositional embryonic development of Amerotyphlops brongersmianus (Vanzolini, 1976) (Serpentes: Typhlopidae) from northeastern Argentina.

The reproductive biology and embryonic development of Typhlopidae have rarely been explored. This family of snakes includes mostly oviparous species with uterine egg retention, but the morphology and development of embryos remain unknown. This work aimed to describe the embryonic development of Amerotyphlops brongersmianus from the northeast of Argentina. For this purpose, embryos from intrauterine eggs of gravid females and eight post-ovipositional eggs incubated in the laboratory were analyzed. Embryonic stages, corresponding to the early, mid and advanced development, and a hatchling were described. The main organs and systems form during the period of intrauterine embryonic retention. Comparing to other snakes, differences in the development of cranial structures such as encephalic vesicles and mandibular and maxillary processes were identified. After oviposition the development and differentiation of the tissues and organs completes, the body scales develop, the characteristic pattern of pigmentation establishes and the embryo grows and consumes the yolk. On average, the incubation period lasts 55 days. Differences in the stage of development at oviposition among females of different populations were observed. Embryonic retention could extend up to advanced stages of development.