This species is often considered the poster child for the amphibian extinction crisis. When the golden toad was discovered in a Costa Rican cloud forest in the late 1960s, researchers observed hundreds of toads breeding in temporary pools at the start of the rainy season. But two decades later the species began to decline precipitously; the last individual, a solitary male, was seen in May 1989.

This amphibian, native to eastern Australia, is famous for its unique mode of reproduction: the females swallow their eggs and raise the tadpoles in their stomachs, eventually giving birth to froglets through their mouths.

Researchers note that during the brooding stage the frogs' stomachs stop producing hydrochloric acid to prevent damaging the tadpoles. This tactic could have been studied by researchers looking for new stomach ulcer treatments; unfortunately, both species of brooding frog are believed to be extinct.

Don't let the name fool you--this toad is actually native to Colombia, and was found near a small village named Mesopotamia. It was last seen in 1914 in a creek, and no photos of the species exist.

Only two specimens of this striking salamander have ever been seen, and one quickly went missing. Scientists first collected the salamander from a Guatemalan forest in 1974, but the amphibian mysteriously vanished during its transit to California--the scientists think it was stolen. Another specimen was seen the following year, but there's been nothing since then.

To seek out the African painted frog, researchers will trek through the highlands of eastern Democratic Republic of Congo and the mountains of western Rwanda, scouring bamboo forests for signs of amphibian life. No photos exist of this species and it hasn't been seen since 1950, but biologists say that may be due to a scarcity of field work.

This species lives on riverbanks and in the lowland rainforest of southwestern Ecuador; it was last seen in 1995. Stubfoot toads have been particularly hard hit by extinctions, and researchers think this species has been devastated by chytrid fungal disease.

The researchers who go in search of the Turkestanian salamander have their work cut out for them. When the species was first seen and collected in 1909, its range was loosely described as being "between Pamir and Samarkand," which means the salamander could be living in Kyrgyzstan, Tajikistan, or Uzbekistan. The intrepid scientists will choose a path based on the areas most suitable for salamanders within the expedition route of the original collector.

This vivid creature has only been spotted in a single stream in an isolated cloud forest in Venezuela. The species was once relatively abundant within its small range, but it hasn't been seen in 20 years.

This frog was last seen in 1955 on the shores of Israel's Lake Huleh. That's around the same time that the Huleh marshes were drained in an effort to wipe out malaria and to convert the land to agricutural use. Biologists will search for the frog in the 5 percent of the wetlands that remained after drainage.