Description: Adult males 22.5-29 mm SVL, adult females 29-32 mm SVL. Head wider than long. Snout is rounded in dorsal view, obtuse in profile. Nares are not protuberant and are directed dorsolaterally. Eyes are large but not protuberant. Interorbital width considerably exceeds the eye diameter. Tympanum is round and indistinct. Vomerine odontophores are round with only a few teeth present, and are located between choanae. Finger I is slightly longer than Finger II. Both finger and toe discs are truncated. Fingers I and II have no webbing in between, but there is vestigial webbing between Fingers II and III, and more developed webbing between Fingers II and IV. Toes are moderately webbed. There is no tarsal fold or tubercle present. No fringing is present on arms or legs. Dorsal skin surfaces are very granular. Males have a large, well-developed white nuptial pad on the dorsal and outer lateral margin of the base of each thumb (Savage 2002).
Coloration is dark blue-green, with scattered black spots usually present. Parietal peritoneal sheath covering anterior internal organs, white pericardium, and white digestive tract are present. Liver is reddish. Bones are dark green. Upper lip has a white stripe. Iris is pale gray-gold (Savage 2002).
Larvae are 11 mm at stage 25 with an elongated and slightly depressed body. Nostrils and eyes are dorsal. Spiracle is located sinistrally and is much closer to the posterior margin of the body than the eye. Vent tube is located in the middle. Mouth is ventral. A complete oral disc, beaks, and 2/3 rows of denticles are present. Lower beak has large blunt serrations. A2 is restricted to two short segments on either side of the mouth. P3 is equal to or only slightly shorter than other posterior tooth rows. A single row of labial papillae is present around the sides and bottom of the oral disc but not above mouth. The tail is long with reduced caudal fins and a round tip (Savage 2002; Lips and Savage 1996).
Larval coloration is black upon hatching. As the tadpole matures it becomes pale brown with translucent fins; the fins have sparse dark spotting toward the posterior (Savage 2002).
The specific epithet granulosa is derived from the Latin word granulum, meaning small-grained or granular, referring to the granular skin of this species (McCranie and Wilson 2002). The karyotype is 2N = 20 (Duellman 1967).
A Spanish-language species account can be found at the website of Instituto Nacional de Biodiversidad (INBio).
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- Duellman, W. E. (1967). ''Additional studies of chromosomes of anuran amphibians.'' Systematic Zoology, 16(1), 38-43.
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- Kubicki, B. (2007). Glass Frogs of Costa Rica/ Rana de Vidrio de Costa Rica. Editorial INBio, Costa Rica.
- Köhler, G. (2001). Anfibios y Reptiles de Nicaragua. Herpeton, Offenbach, Federal Republic of Germany.
- Lips, K. L., and Savage, J. M. (1996). ''Key to the known tadpoles (Amphibia: Anura) of Costa Rica.'' Studies on Neotropical Fauna and Environment, 31, 17-26.
- Solís, F., Ibáñez, R., Jaramillo, C., Chaves, G., Savage, J., Cruz, G., Wilson, L.D., Köhler, G. and Kubicki, B. (2004). Cochranella granulosa. In: IUCN 2009. IUCN Red List of Threatened Species. Version 2009.1. www.iucnredlist.org. Downloaded on 05 October 2009.