Placental structure of the Australian lizard, Niveoscincus metallicus (Squamata: Scincidae)

Abstract

A unique type of reptilian allantoplacenta was described by Weekes [1930] (Proc. Linn. Soc. N.S.W. 55:550–576) from a single embryonic stage of the Tasmanian skink, Niveoscincus ocellatus (as Lygosoma (Liolepisma) ocellatum). She also assigned N. metallicus to this placental category but did not provide a description. Here we provide a description of allantoplacentation and yolk sac placentation of N. metallicus. The allantoplacenta is regionally differentiated and differs from other reptilian allantoplacentae by the presence of a zone of hypertrophied chorionic epithelial cells in apposition to uterine blood vessels which are contained within ridges formed from uterine epithelial cells. This zone is located dorsolaterally along the long axis of the egg at the upper margin of the yolk sac. In contrast, the cells of the chorionic epithelium dorsal to the embryo are smaller and the uterine blood vessels are not contained in ridges. The definitive yolk sac placenta is an omphaloplacenta. The bilaminar omphalopleure of the omphaloplacenta consists of an outer layer of cuboidal or columnar cells. Cells of the uterine epithelium of the omphaloplacenta are cuboidal or columnar in shape and are supported by uterine blood vessels.