Early developmental biology of Platymantis vitiana including supportive evidence of structural specialization unique to the ceratobatrachidae

Direct embryonic development belongs to one of six unique developmental guilds within the endotrophic anurans. Few studies have been conducted on the embryonic development of direct developers. Herein, we present a unique form of embryonic development for direct developers from the genus Platymantis (Family Ceratobtrachidae). We incubated fertile eggs (n=2 egg clutches; 40 eggs per clutch) of the endangered Fijian ground frog Platymantis vitiana under controlled laboratory conditions (25 Celsius and 100% relative humidity). Embryonic development (fertilization to hatching) took on average 29days. Several unique embryonic structures were recorded, including the presence of very large eggs [8.5mm diameter inclusive of egg-jelly and yolk, with the largest yolk diameter (6.0mm) recorded for the genus Platymantis], the complete loss of the usual larval mouthparts, egg-tooth, gill buds and gills. Embryonic structural specialization included large abdominal sacs with blood capillaries which are likely the main medium of gas and waste exchange in P. vitiana. We provide a novel 10-stage staging system of embryonic development for P. vitiana which may also be useful for staging other members of the Platymantis genus. Our study contributes to existing knowledge on the developmental biology of the little studied direct developing endotrophic anurans.