Fish

Coelacanth: Living Fossil
The Coelacanth is a primitive lobe-finned fish that was thought to have gone extinct 200 million years ago. Then, a live one was discovered off the coast of South Africa in 1938. These types of fish are thought to be the ancestors of amphibians. They have the bony armor that ancient fishes had.

Wikipedia entry: http://en.wikipedia.org/wiki/Coelacanth

Mudskipper: Four-eyes
Mudskippers are amphibious fish that spend their lives in muddy marshes. Their eyes are split into four, with the top half of each eye scanning above the water, while the bottom half of each eye views underneath the water.

They are able to breath air while out of the water as long as they keep moist.

Wikipedia entry: http://en.wikipedia.org/wiki/Mudskipper

Archerfish: Sharpshooter
The archerfish has mouth and eye adaptations that allow it to hunt bugs sitting above the water and shoot them down with jets of water.

They are able to compensate for the refraction of light across the air-water boundary and shoot very accurately, while the groove in their mouth and throat allows it to blast water at different velocities simultaneously, such that a large blob of water arrives at the target all at once.

The archerfish is native to brackish waters of south Asia.

See also: http://www.nature.com/news/how-archer-fish-gun-down-prey-from-a-distance-1.15845

Wikipedia entry: http://en.wikipedia.org/wiki/Archerfish

Blind Cave Fish: No Eyes
The Blind Cave Fish is native to caves in Mexico.

As it spends its entire life in the dark, its eyes have no use, so it has lost them as it evolved. It is able to navigate around by detecting vibrations in the water.

Wikipedia entry: http://en.wikipedia.org/wiki/Mexican_tetra

Candiru: Most Feared Fish
The Candiru is generally more feared in the Amazon river basin by natives than the piranha. It is a parasitic catfish that attacks the gills of passing fish. It has a reputation for seeking out waders passing urine into the river, climbing the urine stream, and lodging itself in the urethra of the unfortunate victim using spines that protrude from its head and body. It can only then be removed by surgery. This is something that one should avoid at all costs.

Wikipedia entry: http://en.wikipedia.org/wiki/Candiru

Goliath Tigerfish: Greatest Freshwater Gamefish in the World
The Goliath Tigerfish is the apex predator of the fast-flowing Congo River of Africa. It possesses a massive set of teeth and a nasty disposition.

It is considered the ultimate freshwater gamefish due to the ferocity of its fight and challenge to land.

Wikipedia entry: http://en.wikipedia.org/wiki/Hydrocynus_goliath

Leafy Seadragon: Most Extreme Camouflage
The leafy seadragon is a relative of seahorses that lives off of the south coast of Australia. It has an elaborate set of appendages that allow it to blend in with the drifting seaweed in its native habitat.

It swims without appearing to move its body by undulating a transparent fin on its back.

Wikipedia entry: http://en.wikipedia.org/wiki/Leafy_seadragon

Goblin Shark: Alien Jaws
The Goblin Shark is a living fossil, the only member of its ancient family that survives.

It has a long snout with extensible jaws that can be snapped forward.

Goblin sharks are not a threat to humans despite their garish appearance.

Wikipedia entry: http://en.wikipedia.org/wiki/Goblin_shark

Chimaera: Most Ancient Fish
The chimaera is thought to be the most ancient lineage of fishes still alive today.

They look weird.

Wikipedia entry: http://en.wikipedia.org/wiki/Chimaera

Hagfish: Most Primitive Fish
The hagfish is considered to be the most primitive fish in the ocean. They have a skull, but no vertebral column. They are jawless. When threatened, the hagfish emits copious amounts of slime, which makes it distasteful to predators. It is able to tie itself into a knot, in order to clean itself of slime. Hagfish are scavengers of dead animals on the seafloor.

Wikipedia entry: http://en.wikipedia.org/wiki/Hagfish

Barreleye: Transparent Head
The barreleye has a transparent head, with eyes that peer upwards to detect prey silhouetted against the light coming from the surface of the ocean. They are able to rotate their eyes from forward to gazing upwards inside their transparent dome heads.

One species is the only vertebrate that uses a mirror in its eye to collect light in addition to a lens.

Wikipedia entry: https://en.wikipedia.org/wiki/Barreleye

Oarfish: Largest Bony Fish
The oarfish is a large, long fish that lives at great depths. It is thought to have inspired sailor's tales about sea serpents.

Until 2001, it had never been seen alive. It has since been filmed at depth.

Wikipedia entry: http://en.wikipedia.org/wiki/Oarfish