The two-fingered skink is a ‘sand-swimmer’ with reduced limbs, closed ear holes, and a streamlined body — allowing it to move through sand at speed. It is rarely seen above the surface.

Malagasy leaf-nosed snakes possess bizarre nasal protrusions that mimic smooth vines or frilly leaves and broken branches — depending on the sex and species. These snakes can grow over a metre (3.3 ft) long, but are extremely cryptic and difficult to spot in both dry and wet forests. 

The South Georgia pipit is the only songbird in the Antarctic region proper and the most southern-breeding of all 6,500+ passerine species. It survives the island’s extreme winds and freezing temperatures by sheltering in stands of tussac grass. However, it was nearly wiped out by a rodent infestation.

The breeding plumage of a male red avadavat is a deep scarlet, flecked with dots of white — the species is also known as the “strawberry finch.” To court a female, a male bows deeply and repeatedly, holding a blade of grass or feather in his beak.

The Bonin white-eye is endemic to the isolated Bonin Islands of Japan. On these islands, which are bereft of several types of birds, this white-eye evolved to occupy their niches: foraging among branches like a tit, on trunks like a woodpecker, and on the ground like a robin.

The cave angel is a pale and eyeless fish endemic to a few limestone caves in northwestern Thailand. It’s the only known living fish with a pelvic girdle fused to its spine — structurally similar to early land vertebrates — giving it the ability to “walk” up waterfalls.

The Nosy Hara leaf chameleon, endemic to a tiny Malagasy islet, is one of the smallest chameleons in the world and one of the smallest of all known amniotes (reptiles, birds and mammals). Its maximum length is no more than 3 centimetres (~1.2 in) — about the size of a paper clip.

The cuckoo-roller is a relic species: the sole living member of the order Leptosomiformes — for comparison, other bird orders can contain hundreds of species, while Passeriformes (a.k.a. songbirds) has over 6,500. And, despite its name, the cuckoo-roller is not closely related to cuckoos nor rollers.

The hooded pitohui is one of the few known toxic birds. Like poison dart frogs, it builds up toxins in its body — likely from beetles that it eats — storing them most potently in its feathers which can cause an itching, burning, and numbing sensation when touched.

The olm is a blind salamander found only in the caves of the Dinaric Alps. Like the axolotl, it never metamorphoses, and its maximum lifespan has been estimated at ~102 years. Olms would occasionally wash out of caves during floods and were once believed to be baby dragons in Slovenia.

The Okinawa rail is Japan's only flightless bird — found exclusively on the island of Okinawa. Before nightfall, it uses its powerful clawed feet to climb trees, where it sleeps to avoid nocturnal-hunting pit vipers. In the morning, it drops back down in a graceless fluttering of wings.

The island canary — native to the Canary Islands, Madeira, and the Azores — is the wild ancestor of the domestic canary. It was bred to be garishly coloured, to have different haircuts and postures, and to imitate the songs of other birds or the sound of babbling water. Later, it was used to detect dangerous gases in coal mines.

The white-rumped vulture was once India’s most common vulture — and perhaps the most numerous large bird of prey in the world. But between the mid-1990s and 2006, its population plummeted by 99.9%, and it’s now considered critically endangered.

The desmans are the odd duo out in the mole family. Both are semi-aquatic: the Russian desman lives in slow-moving waters, while the Pyrenean prefers fast-moving mountain streams. Desmans were more numerous once, but today these are the last two species left.

The Kauaʻi cave wolf spider has adapted to the lightless caverns of southern Kauaʻi by losing its eyes entirely. It creeps slowly — consuming ~40% as much oxygen as surface-dwelling wolf spiders — pursuing its primary prey: the Kauaʻi cave amphipod, a blind crustacean endemic to the same caves.

The raccoon dog isn’t a raccoon at all — it’s a canid, more closely related to foxes. It’s the only member of the dog family that hibernates and one of the few to use communal latrines, where it leaves behind smelly “messages” about its diet, health, and breeding status for other raccoon dogs to sniff out.

The white-tipped sicklebill uses its extremely decurved bill to reach inside sharply curved flowers, allowing it to drink nectar other nectarivores cannot reach. It is also a ‘trapliner’ — repeating the same foraging circuits, visiting favourite flowers along its particular route.

The immortal jellyfish is so-called because it can revert to a previous stage in its life cycle due to stress or injury. However, this isn't immortality as we typically think of it: the jelly turns back into a stationary polyp that spawns several genetically identical medusae.

The Kangaroo Island dunnart lives only on Kangaroo Island, off South Australia. In 2019–2020, catastrophic bushfires swept across the island, burning over 90% of the dunnart’s habitat. The species was feared extinct, but a few were found to have survived — perhaps just 50–100 individuals.

The eastern and western meadowlarks look nearly identical, behave in the same way, and share similar habitats — even overlapping in range in the central plains of North America — yet they are separate species that rarely interbreed. What keeps them apart are the different songs they sing.