Embryonic staging table for a direct-developing salamander, Plethodon cinereus (Plethodontidae).

This work presents a refined staging table for the direct-developing red-backed salamander Plethodon cinereus, which is based on the incomplete staging system of James Norman Dent (J Morphol 1942; 71:577-601). This common species from eastern North America is a member of the species-rich lungless salamander family Plethodontidae. The staging table presented here covers several stages omitted by Dent and reveals novel developmental features of P. cinereus embryos. These include putative Leydig cells and open gill clefts, which are found in larvae of metamorphosing species but were previously reported as absent in direct-developing Plethodon. Other features found in larvae of metamorphosing salamander species, such as the palatopterygoid bone and lateral line neuromasts, were not observed in this material. The occurrence of larval and metamorphic features in these embryos has direct bearing on the patterns of life history evolution within the plethodontidae family. This study emphasizes the degree to which typically larval structures are retained in this direct-developing species and provides a staging table for further investigations into the development and evolution of plethodontid salamanders.