Under permanent ice cover that is hundreds of meters thick in Antarctica, researchers have discovered sessile animals (similar to sponges) that have adapted to extreme conditions like darkness and subzero temperatures, as well as being under such expanses of ice that these organisms are 260 kilometers (155 miles) from the open sea. To what species the rock-bound creatures belong remains unclear.

It looks like a seahorse — but it's a red sea dragon, a rare marine fish. Researchers off the coast of Western Australia have only recently been able to admire these live specimens, which were identified in 2015. The animals were observed feeding at a depth of 50 meters (165 feet).

The "real" seahorses are also quite unusual. They are one of the few species to swim vertically. But this doesn't work out too well, so they are just poor swimmers. The males carry fertilized eggs and give birth to their young.

Despite its name, an electric eel is not an eel but a knife fish. It is indeed electric, though, and generates powerful electric shocks of up to 600 volts to kill prey. Researchers have learned that the fish also uses its high-voltage discharge as a high-precision tracking device — similar to the echolocation calls of bats.

Banded archerfish live in brackish water and have come up with a unique way to kill prey: They spit a jet of water into the air to shoot down insects. Larger fish may even hit targets up to 3 meters away.

This fish buries itself in the sand and waits till its prey passes its head. Then it shoots upward and gets its meal. Stargazers have top-mounted eyes and a large, upward-facing mouth. If you ever see one, be careful: The species is venomous.

Venomous and good at hiding? The stonefish is both! The species looks exactly like a stone overgrown with algae. But step on it and you will come to know its needlelike venomous spines. It can even be fatal for humans.

Puffer fish have an elastic stomach that they can fill with water when feeling threatened. This way they become much larger and almost spherical in shape. They produce the tetrodotoxin, which can kill humans. In Japan, people eat puffer fish.

An anglerfish attracts its prey with an illicium, or a fleshy growth from its head. The tip of the illicium illuminates to make prey curious — and then they are swallowed up by the huge mouth of the predator. Anglerfish can be found almost anywhere in the world, including the deep sea.

With high pressure, almost no light and little food, animals have to be especially adapted to be able to live in the deep sea. Viperfish need to make absolutely sure that they don't miss a meal — that's what the huge mouth and the sharp teeth are for.

The plaice is a flatfish — no doubt about that. The well-camouflaged fish bury themselves in the sediment. They develop so that both eyes end up on the same side of the head.

Mudskippers apparently couldn't decide whether they liked land or water more. So they compromised and chose intertidal habitats. They are definitely fish but can use their pectoral fins to walk on land. They can breathe through their skin like amphibians.

Researchers believe that the flat, sideways extended head gives hammerhead sharks a higher visual field. That helps them find their prey.