Although there are many diminutive Dendrobatids, the term “thumbnail” is reserved for members of the genus Ranitomeya. These are typically small, smooth, iridescent inhabitants of the Amazonian rainforest.
To date, Ranitomeya is comprised of the following species:
Ranitomeya amazonica (Schulte, 1999)
Ranitomeya benedicta (Brown et al., 2008)
Ranitomeya cyanovittata (Perez-Pena, et al., 2010)
Ranitomeya defleri (Twomey and Brown, 2009)
Ranitomeya fantastica (Boulanger, 1883)
Ranitomeya flavovittata (Schulte, 1999)
Ranitomey imitator (Schulte, 1986)
Ranitomeya reticulate (Boulanger, 1883)
Ranitomeya sirensis (Aichinger, 1991)
Ranitomeya summersi (Brown et al., 2008)
Ranitomeya torero (Brown and Twomey et al., 2011)
Ranitomeya uakarii ( Brown et al., 2006)
Ranitomeya vanzolinii (Myers, 1982)
Ranitomeya variabilis (Zimmermann and Zimmermann, 1988)
Ranitomeya ventrimaculata (Shreve, 1935)
Ranitomeya yavaricola (Perez-Pena et al. 2010)
Amazon Basin and marginal areas of adjacent, disturbed and fragmented forest regions.
Rana: Latin for “frog”; also, Ranita: Spanish for small frog; Tomeya, named for a frog keeper named W. A. Tomey 
Species of the genus Ranitomeya are quite diverse in habit and habitat. All are skilled climbers, although some are more arboreal than others. Still others are essentially terrestrial. Some are considerably bold and even entertaining (certain imitator morphs come to mind), while others, can be somewhat shy. It is also interesting to note that some Ranitomeya are facultative egg-feeders, meaning that the females will deposit nutritive eggs for their omnivorous tadpoles, while others abandon their young after transporting them to water. The eggs and the tadpoles of most are quite large when compared to those of Oophaga species of similar size.
 Species authority information from dendrobates.org: http://www.dendrobates.org/ranitomeya.html
 Lötters, S; Jungfer, KH; Henkel, FW; Schmidt, W: Poison Frogs Biology, Species and Captive Husbandry, 2007 Chimaira Buchhandelsesellschaft mbH