Glass Frogs: Centrolenidae

In many of the species of glass frogs, the beating heart, other working organs, blood vessels, and the bones inside are clearly visible through their see-through, or transparent, undersides. Even from the top in many species, the frogs' bodies have the look of frosted glass and sometimes provide a glimpse of the animals' inner workings. In fact, the descriptions of some species include the size of their organs. The view from the topside is not as good as it is from the bottom, because the frog has thick muscles on its back that hide the organs from sight.

Most of the glass frogs are shades of green, although some are brown. Many have tiny spots, which are called ocelli (oh-CELL-ee). These ocelli in frogs should not be confused with the ocelli in insects. In insects, ocelli look like the spots on a frog's back, but they are actually tiny eyes. Lynch's Cochran frog, for instance, may be brownish green or tan and has black ocelli that are tipped in orange or yellow. It also has white warts. The Nicaraguan glass frog is green, sometimes with numerous black spots on its head, back, and legs. In the Atrato glass frog, the back is yellow green with small brown spots in all but a few large, round patches on its head, back, and legs. Regardless of their color or pattern, most glass frogs are extremely hard to see when they sit on green leaves. They almost look as if they melt into the leaves and become a part of them.

Since the bones are visible from the outside in most glass frogs, the color of the bones also helps to tell some species apart. The bones in the Pichincha glass frog, Pacific giant glass frog, Ecuador Cochran frog, and many others, are green. In the Atrato glass frog, Fleischmann's glass frog, and La Palma glass frog, among others, the bones are white.

The typical glass frog has a delicate body that looks as if it would easily break if handled. These slender, and often very smooth, bodies have thin front and rear legs. Some species, like the grainy Cochran frog, have hundreds of tiny bumps on their heads and backs. All of their toe bones are T-shaped at the ends. On the outside, the toes are tipped with wide, rounded pads. Thin, transparent webs stretch between their toes.

The head in the average glass frog has large bulging eyes that face mostly forward rather than to the sides and are located more toward the top of the head than the eyes in most other frogs. In many frog species, the head blends into the body and does not appear to have a neck between the head and body. The typical glass frog's head, on the other hand, is obvious, even looking round when viewed from above.

Most members of this family are small, reaching 0.7 to 1.2 inches (1.8 to 3 centimeters) from the tip of the snout to the end of the rump. Males in many species are smaller than females. In the Pichincha glass frog, for example, females grow to 1.3 inches (3.23 centimeters) long, while males reach 1.1 to 1.2 inches (2.68 to 3.15 centimeters) in length. The Nicaragua glass frog is similar. The female in this species reaches 1.0 to 1.1 inches (2.54 to 2.68 centimeters) long, while the male grows to 0.9 to 1.1 inches (2.17 to 2.68 centimeters) in length. In other species, like the Ecuador Cochran frog, the males are the larger of the two. Female Ecuador Cochran frogs reach 0.8 to 1.0 inches (2 to 2.54 centimeters) in length, while males can grow to 1.9 inches (4.83 centimeters) long. The Pacific giant glass frog is truly a giant among glass frogs. Although not large when compared to frogs in some other families, the male's 3.2-inch (8.13-centimeter) body makes it the biggest of the glass frogs. Female Pacific giant glass frogs are not quite as large, but they are still giants compared to most other glass frogs. Females can reach 2.4 to 2.9 inches (6.09 to 7.36 centimeters) in length.