Scientists discovered this new species of "glass frog" in Ecuador's Amazon lowlands. Hyalinobatrachium yaku's belly is so transparent that you can clearly see its kidneys, bladder, and beating heart. From Science News:
Yaku means "water" in Kichwa, a language spoken in Ecuador and parts of Peru where H. yaku may also live. Glass frogs, like most amphibians, depend on streams. Egg clutches dangle on the underside of leaves, then hatch, and the tadpoles drop into the water below. But the frogs are threatened by pollution and habitat destruction, the researchers write. Oil extraction, which occurs in about 70 percent of Ecuador's Amazon rainforest, and expanding mining activities are both concerns.
"A marvelous new glassfrog (Centrolenidae, Hyalinobatrachium) from Amazonian Ecuador" (ZooKeys)