The Developmental Stages of the Sphagnum Frog, Kyarranus-Sphagnicolus Moore (Anura, Myobatrachidae)

Abstract

The external features of development of the sphagnum frog, Kyarranus sphagnicolus, 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, under stones on the forest floor and in similar wet situations. Field-collected spawn was raised at constant temperature. Duration of development 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 is 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 gastrulation. Neurular rotation was not observed. Later development results in a normal-looking but nonfeeding tadpole with reduced mouth parts. The hindlimb rudiments appear precociously shortly after the heartbeat stage. The tadpoles possess an extensive but transitory vitelline circulation which may have a respiratory function, are relative immobile and metamorphose within the nest. The dorsal caudal venous return is carried by hitherto unreported superficial vessels, the 'dorsal vitelline veins'. In K. sphagnicolus terrestrial oviposition is followed by the completion of tadpole development within the nest. This mode of anuran development occurs also on other continents, but in Australia is unique to the closely related genera Kyarranus and Philoria.