Morphology and ultrastructure of the chorioallantoic placenta of the Iberian mole (Talpa occidentalis) with special reference to heterophagous areolas and the nature of interhaemal barrier.

This study provides a contribution to the reconstruction of the eulipotyphlan placental morphotype and also may help resolving a long-standing conflict about the interhaemal barrier in moles. As detailed descriptions of talpid placentation, only available for Talpa europaea and Scalopus aquaticus, led to a controversial debate on the nature of interhaemal barrier, the collection of more placental data of further mole species was strongly desired. Hence, the placentas of six gestational stages of Talpa occidentalis have been studied concerning their morphogenesis and ultrastructure with special focus on the structure of the interhaemal barrier and heterophagous regions. Generally, the mode of placentation in T. occidentalis resembles that of T. europaea, including a broad, discoid, antimesometrial, definitive chorioallantoic placenta of labyrinthine type being still villous in earlier stages. Within the labyrinth, the zona intima shows an endotheliochorial interhaemal barrier with a two-layered trophoblast. This clearly contradicts former statements on the S. aquaticus placenta made by Prasad et al. (1979), although their findings cannot exclude a totally different interpretation. Regardless, the placenta of moles represents the least invasive mode of placentation among Eulipotyphla, which otherwise have highly invasive placentas. Although the phagocytic areolas situated above uterine gland openings are heterophagous, they mainly seem to serve fetal histiotrophic nutrition, at least early in pregnancy. In later stages the number of glands and areolas decreases. This special type of additional phagocytic region is usually most common in species with noninvasive, epitheliochorial placentation, which suggests a correlation between placental invasiveness and the occurrence and type of phagocytic placental structures. The compact and invasive mode of placentation of Talpidae and all other Eulipotyphla seems to be plesiomorphic within Laurasiatheria and is always correlated with an altricial neonate.