THE DEVELOPMENTAL STAGES OF THE SPHAGNUM FROG, KYARRANUS-SPHAGNICOLUSMOORE (ANURA, MYOBATRACHIDAE)

The external features of development of the sphagnum frog, Kyarranus s phagnicolus, are described. K. sphagnicolus produces large unpigmented eggs (3.35 +/- 0.21 mm). The mean number of eggs per clutch was 58-3 (range 30-91). The eggs are embedded in a foamy jelly and deposited in a shallow burrow excavated by the male in clumps of sphagnum moss, un der stones on the forest floor and in similar wet situations. Field-co llected spawn was raised at constant temperature. Duration of developm ent is approximately 55 days at 18-degrees-C and 80 days at 15-degrees -C. Cleavage is holoblastic and unequal and the third cleavage plane i s vertical, as in many large-yolked amphibians. The animal hemisphere of the blastula is unpigmented and semitransparent and permits direct observation of the involution of the chorda-mesoderm during gastrulati on. Neurular rotation was not observed. Later development results in a normal-looking but nonfeeding tadpole with reduced mouth parts. The h indlimb rudiments appear precociously shortly after the heartbeat stag e. The tadpoles possess an extensive but transitory vitelline circulat ion which may have a respiratory function, are relative immobile and m etamorphose within the nest. The dorsal caudal venous return is carrie d by hitherto unreported superficial vessels, the 'dorsal vitelline ve ins'. In K. sphagnicolus terrestrial oviposition is followed by the co mpletion of tadpole development within the nest. This mode of anuran d evelopment occurs also on other continents, but in Australia is unique to the closely related genera Kyarranus and Philoria.