Somitogenesis in the marsupial frog Gastrotheca riobambae.

This paper reports the first description of somitogenesis in a non-aquatic-developing amphibian, the Andean marsupial frog, Gastrotheca riobambae. This frog develops from an embryonic disk located on top of a large yolky egg, bearing some resemblance to the embryo of the chick. Besides the histological characterization of somite formation, we quantified cell number in the developing somites of Gastrotheca, Xenopus laevis and the chick. Gastrotheca was found to have a mode of somitogenesis which has previously been encountered in the aquatic-developing toad Bombina. Somitic cell number was found to be an order of magnitude higher than that of Xenopus, and approximately double that of the chick. We discuss the possible relation between mode of somitogenesis, somitic cell number, speed of development and egg size.