Placentation in a xenarthran species, the giant anteater Myrmecophaga tridactyla
, as derived from [45
]. (a) The placenta consisted of villous and trabecula areas that both reached the decidua. (b) Clusters of proliferative trophoblast cells (white arrows) are frequent in the trabeculae and the tips of the villi that included fetal capillaries (black arrows). Immunostaining for PCNA. (c) The villi surface is syncytial without remnants of the maternal capillary endothelium, revealed by negative response to immunostaining for vimentin, built by syncytial and cellular trophoblast. Inside is hypertrophied mesenchyme. ct = cellular trophoblast, dec = decidua, INS = intervillous space, mc = maternal capillary, Syn = syncytiotrophoblast, trab = trabeculae, and villi = villous area of the placenta.