CentrolenidaeGlass Frogs, Leaf Frogs

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More than 100 species exist in three genera within this family of translucent-skinned tree frogs. Because of the difficulty in finding these frogs, new species are regularly being described, and the family is growing. Distribution is limited to the humid neotropics, with the greatest diversity on the slopes of the Andes, as well as in Costa Rica and Panama.

Glass frogs are so named for the transparent skin on their venters, which allows for the observation of their viscera. Dorsally they tend to be green, with yellow, white, blue or red markings. Like most arboreal frogs, they have T-shaped terminal phalanges (expanded digit tips) and an intercalary cartilage between the terminal and penultimate phalanges of each digit. Commonly cited synapomorphies uniting this group include the fusion of the astragalus and calcaneum into a single element (convergent with Pelodytes), and an expanded medial process on the third metacarpal. Additional characters which are present but do not diagnose the family include a complete cricoid ring, teeth on both the maxillae and premaxillae, horizontal pupils, expanded sacral diapophyses, the presence of eight holochordal-procoelous presacral vertebrae, and axillary amplexus. Most species are smaller than 30 mm total body length; the notable exception is Centrolene gekkoideum (77 mm). Diploid number is 20.

Glass frogs live high in trees overhanging mountain streams. Parental care is common -- perhaps even ubiquitous -- among glass frogs, and males sometime guard multiple clutches. Small clutches of eggs are laid above the water on leaves, rocks, or bromeliads. When the type IV tadpoles hatch, they fall into the water below, and live in the muck and leaf litter on the bottoms of streams. Tadpoles living in oxygen-poor habitats are sometimes bright red as a result of blood flow close to the surface of their unpigmented skin. The call of glass frogs is a high peep (rather like that of fine crystal) or whistle. In some species, the call of a single individual may imitate a chorus. Some green centrolenids reflect light in the infrared spectrum, which may play a part in thermoregulation.

Glass frogs are members of the Neobatrachia, the relationships of which are highly controversial. Most authors identify a superfamily, alternately called Bufonoidea or Hyloidea, which includes all the neobatrachians that are neither Ranoids nor Microhyloids. The group Bufonoidea is thus sketchy at best. Furthermore, most relationships among the bufonoids are not resolved. However, several researchers have presented evidence that Pseudidae, Hylidae and Centrolenidae are a monophyletic group, based largely on the shared presence of intercalary elements. Separate research has proposed a hylid - centrolenid relationship (excluding Pseudidae), and others have proposed a hylid - centrolenid - bufonid clade. Regardless, it does appear that Centrolenidae is itself a monophyletic group, even though the genera within the family are being reassigned (e.g. the genus Centrolenella has recently been completely replaced).

No fossil centrolenids are known.

Cannatella, D. 1996. Centrolenidae: Tree of Life. (Website.) http://tolweb.org/tree?group=Centrolenidae&contgroup=Neobatrachia

Cogger, H. G., and R. G. Zweifel, editors. 1998. Encyclopedia of Reptiles and Amphibians, 2nd edition. Academic Press, San Diego.

Duellman, W. E., and L. Trueb. 1986. Biology of Amphibians. Johns Hopkins University Press, Baltimore, MD.

Pough, F. H., R. M. Andrews, J. E. Cadle, M. L. Crump, A. H. Savitzky, and K. D. Wells. 1998. Herpetology. Prentice-Hall, Inc., Upper Saddle River, NJ.

Stebbins, R. C., and N. W. Cohen. 1995. A natural history of amphibians. Princeton University Press, Princeton.

Zug, G. R. 1993. Herpetology: an introductory biology of amphibians and reptiles. Academic Press, San Diego.

Contributors

Heather Heying (author).

Glossary

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

metamorphosis

A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.

motile

having the capacity to move from one place to another.