Glass frogs derive their name from the observation in that several the skin is almost transparent, and once can see the internal organs, and even observe the heart beating in some species. The Glass Frogs are a large group of rather similar species. They are mostly arboreal, living high in trees overhanging mountain streams in Mexico, Central, and South America. With the exception of Centrolene gekkoideum most species are small, about 20-30 mm long. Until the recent work of Ruiz-Carranza and Lynch (1991), all of the small species were called Centrolenella; that name is no longer used.
The call of Glass Frogs is a high peep or whistle. In some species, a single individual seems to initiate a chorus, in which a wave of calls seems to travel along the stream. Centrolenids lay their clutches of eggs on vegetation, usually several meters above a stream (one high montane species, Centrolene buckleyi, uses bromeliads to hide their eggs). When the eggs hatch, the tadpoles fall into the water; or, if they miss the water, they use their muscular tails to flip themselves into the water. The tadpoles generally burrow into the stream substrate. In some species the males position themselves over the egg mass, apparently guarding it from predators, including "frog flies" which lay their eggs in the frog's egg mass. The developing fly larvae are known to parasitize and destroy clutches of eggs (Villa and Townsend, 1983).
Because they inhabit high montane streams, glass frogs are not collected casually; of the 64 species listed in Frost (1985), only 23 were described before 1960, and many more have been described since 1985. The exploration of new streams along the Andes of South American almost certainly yields new species.
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