Meeting Abstract

P2.112  Monday, Jan. 5  Scanning EM of the Placental Membranes in the Viviparous Lizard Sceloporus jarrovi ANDERSON, K.E.; BLACKBURN, D.G. **; DUNLAP, K.D.; Trinity College, Hartford CT daniel.blackburn@trincoll.edu

In viviparous lizards, placentas sustain the developing embryos inside the pregnant female through gas exchange and provision of nutrients. We used scanning EM to reveal the fetal – maternal interface in the spiny lizard Sceloporus jarrovi (Phrynosomatidae) during the last trimester of gestation. Two distinct placentas are formed and persist until parturition. The allantoplacenta consists of the chorioallantois in direct apposition to the uterine epithelium. SEM reveals that fetal and maternal epithelia at the placental interface are highly attenuated, but not eroded, and lack surface specializations. The yolk sac placenta consists of an avascular omphalopleure (with its isolated yolk mass) in conjunction with the uterus. The omphalopleure forms elaborate folds, consisting of epithelium and yolk droplets. These folds protrude into a thick mass of material in the uterine lumen, formed from degenerating shell membrane, cellular debris, and yolk. Scanning EM indicates that this material is sequestered into a restricted, elongated region at the ventral pole, possibly to free up adjacent regions for placental exchange. The presence of elaborate placental specializations in a generalized viviparous lizard is unexpected, and underscores the need for continued explorations of placental diversity in the numerous clades of viviparous squamates.