Adult males 66 to 81 mm SVL. Adult female 77 mm SVL. The smooth dorsal surface has 8 to 12 low transverse ridges. The head is broader than long. From above the snout is blunt and rounded, and in profile is obtuse. The skull is not co-ossified to the skin, but is exostosed. The upper eyelid has a triangular dermal flap. The tympanum is indistinct and measures less than half the diameter of the eye. Finger discs are large, with the disc of finger III equal in size to half the tympanum diameter, and fingers have hardly any webbing. Hindlegs are long. The toes have a moderate amount of webbing. The inner metatarsal tubercle is small and ovoid and the outer metarsal tubercle is lacking. The inner tarsal fold is weakly developed. A triangular calcar is present on the heel. Females have a brood pouch opening on the dorsum, halfway between the sacral hump and vent. Males have no vocal slits but do have a single internal subgular vocal sac that is slightly distensible. On the base of the thumb, in adult males, there is a horny nonspinous brown nuptial pad (Savage 2002).
Ground coloration is dark brown by day and tan at night; this species undergoes metachrosis (color change). Also at night, the light cream to yellow suborbital spot disappears. Unchanging aspects of the coloration include 8-15 narrow, dark brown dorsal transverse lines. Lips are barred. A broad dark brown dorsolateral stripe runs from the tympanum to the groin. The posterior thigh is pale brown. Ventral surfaces are pinkish to pale brown, with the throat being brown. The iris is bronze peripherally, and creamy yellow or olive green medially (Savage 2002).
This frog develops directly into froglets; embryos are thus lacking many morphological features of free-living tadpoles, such as keratinized mouthparts. For a detailed discussion of the morphology of G. cornuta embryos compared to those of several other Gastrotheca species, see Wassersug and Duellman (2004). Gastrotheca embryos have specialized structures called bell gills, which cover 100% of the embryo as it develops within a single chamber in the female's multichambered dorsal brood pouch (del Pino and Escobar 1981).
A Spanish-language species account can be found at the website of Instituto Nacional de Biodiversidad (INBio).
- Coloma, L.A., Ron, S., Jungfer, K-H., Grant, T., Cisneros-Heredia, D., SolÃs, F., IbÃ¡Ã±ez, R., Chaves, G., Savage, J., Jaramillo, C., Fuenmayor, Q., BolaÃ±os, F., Lips, K., Lynch, J.D., and AlmendÃ¡riz, A. (2008). Gastrotheca cornuta. In: IUCN 2009. IUCN Red List of Threatened Species. Version 2009.1. www.iucnredlist.org. Downloaded on 28 July 2009.
- Savage, J. M. (2002). The Amphibians and Reptiles of Costa Rica. University of Chicago Press, Chicago and London.
- Wassersug, R. J., and Duellman, W. E. (1984). ''Oral structures and their development in egg-brooding hylid frog embryos: evolutionary and ecological implications.'' Journal of Morphology , 182, 1-37.
- del Pino, E. (1980). ''Morphology of the pouch and incubatory integument in marsupial frogs (Hylidae).'' Copeia, 1980, 10-17.
- del Pino, E. M. and Escobar, B. (1981). ''Embryonic stages of Gastrotheca riobambae (Fowler) during maternal incubation and comparison with development of other marsupial frogs.'' Journal of Morphology, 167, 277-295.
- del Pino, E., and Humphries, A. A., Jr. (1978). ''Multiple nuclei during early oogenesis in Flectonotus pygmaeus and other marsupial frogs.'' Biological Bulletin, 154, 198-212.