Freshwater
Adapted to inland rivers, creeks, and lakes, pumping out excess water through specialized kidney filtration.
Kodiak Bear
Isolated on one Alaskan island chain for about twelve thousand years, with adult males weighing 600 to 1,400 pounds and standing up to ten feet on their hind legs.
Koi
A pet carp bred into over 100 colour varieties that, in one study, sought out a human hand.
Mandarin Duck
The tree-hole nesting duck whose drake grows an enlarged, brightly colored sail feather every breeding season.
Muskrat
A marsh rodent that builds its home from piled-up plants and eats about a third of its own weight every day.
Mute Swan
Not actually mute: it hisses, snorts and twirls with its wings raised.
Nile Crocodile
An armored crocodile whose skin is more touch-sensitive than a primate's fingertips.
Nile Tilapia
A mouth-brooding cichlid; in one lab strain, a Y-chromosome gene proved essential for maleness.
North American Beaver
Self-sharpening orange teeth strengthened with iron, and an ecosystem engineer that dams streams into ponds.
Northern Pike
A freshwater ambush predator that lies cocked in an S, then strikes with a sprint.
Olm
The cave salamander with eyes buried under its skin, a predicted lifespan past 100 years, and an experimental fast of a year and a half.
Osprey
The fish-hawk that hovers over water, then plunges feet first to grab a fish in its talons.
Pacific Giant Salamander
North America's largest terrestrial salamander, guarding Pacific Northwest streams with a startled bark, a noxious tail secretion, and gills it can keep for life.
Planarian
A freshwater flatworm whose tail can turn into a head when one gene is switched off.
Proboscis Monkey
An oversized nose that works as both a visual badge and a vocal amplifier, webbed fingers and toes that help it swim across rivers, and a cow-like habit of bringing food back up to chew it again.
Pygmy Hippopotamus
Dwarf solitary forest hippo of the Upper Guinean swamps, with pink blood-sweat sunscreen.
Quokka
A Western Australian wallaby with three kinds of colour cone, a permanent grin, and no fear of tourists.
Rainbow Trout
A stream fish whose sex is set by a Y-chromosome gene unrelated to any known sex-differentiating gene.
Red-Bellied Piranha
Razor-sharp interlocking teeth, a red belly, and a school that doubles as cover from predators.
Red-Eared Slider
Whether a slider hatches male or female depends on how warm its nest was.
Reticulated Python
The longest python, up to 33 feet of snake with black X's running down its back in a diamond-like pattern.
Saltwater Crocodile
Up to 23-foot apex archosaur, and the species behind the highest bite force measured in any animal: 3,689 pounds.
Shoebill Stork
Prehistoric-looking swamp stalker with a foot-long bill shaped like a clog.
Siamese Fighting Fish
A fish up to 6.5 cm long that breathes air through a labyrinth organ, and whose males flare their gill covers at each other.
Signal Crayfish
A plague-resistant crayfish brought to Europe to supplement stocks the plague decimated, and a carrier of the disease itself.