Glass Frog

This little guy gets his name from his translucent abdomen. While this class of frogs is primarily lime green, their bellies, and on some even their backs, are see-through so that their heart, intestines and liver are visible through the thin clear skin. While hanging out in the forest, their unique skin gives them the useful ability to blend right into the leaves.
There are 134 species of glass frogs, all between 1.4 and 3 centimeters, and of that number, 60 are considered threatened. They can be found in rainforests in Central and South America.