The Earth's oceans contain half of all species on the planet, and some of the creatures are almost too bizarre to believe. More than a few look like monsters from science fiction novels or aliens from galaxies far away. From a cartoon-like octopus to the miserable-looking blobfish, marine life can range from simply adorable to downright terrifying.
Click through to see 15 of the planet's most bizarre sea creatures.
The red-lipped batfish doesn't need lipstick to make its puckers stand out. The crusty bottom-dweller's naturally bright red mouth is thought to be an adaptation for helping enhance species recognition during mating.
Don't let those kissable lips fool you: The batfish doesn't just sit around looking pretty. It preys on small fish, shrimp, mollusks and crabs. Batfish are found in the deep sea near the Galapagos Islands and have modified fins that enable them to walk along the sea floor.
Take a close look at the head on this guy: You can see right through it. Oddly, the Pacific barreleye has a transparent skull that allows the fish to look both straight ahead and straight up (through its fluid-filled dome). It lives between 400 and 2,500 feet under water, and its eyes are adapted for collecting light deep below the surface. This mad scientist of a fish lives in temperate waters of the Atlantic, Pacific and Indian Oceans.
Take one look at the blobfish and you can guess how it got the name. The deepsea fish composed mostly of gelatinous mass lives in the South Pacific roughly 2,000 to 3,900 feet down. Blobfish don't have much muscle, so they float around the sea floor and swallow anything edible in their path.
Unfortunately for the frown-faced fish, bottom trawling is common in its native Australia and New Zealand. While fishing for more palatable creatures like lobster and crab, fishermen are also snagging blobfish. Overfishing has caused their numbers to dwindle, and blobfish now face extinction.
The frill shark has a large mouth with 25 rows of 300 sharp teeth, six pairs of fringed gill slits, and a long, eel-like body that can grow up to 6 feet long. It's referred to as a "living fossil" because it's a member of one of the oldest living shark species.
Because frill sharks live on the sea floor up to 5,000 feet deep, they are rarely seen alive. But in January 2007, a Japanese fisherman saw a sick frill shark swimming near the water's surface in Tokyo. The shark was caught and transfered to the Awashima Marine Park where it was photographed before dying. That's the shark you see here.
Also known as ghostsharks, ratfish and rabbitfish, chimaera are cartilaginous fish that can live as deep as 8,000 feet under water. Fossil records show that chimaera are one of the oldest groups of fish alive today, and they've remained mostly unchanged since the age of dinosaurs.
Deep Sea Comb Jelly
The deep sea comb jelly (nicknamed Sunkist jelly) is about the size and color of an orange. These jellies have rows of hair-like cilia for swimming and two white, sticky, curled tentacles for snatching prey. They're rare, found mainly in the deep waters off California and the North Atlantic Ocean.
The ocean sunfish, or Mola mola, looks likes a creature from outerspace with its enormous flat, circular body and truncated back fin. It's the heaviest bony fish in the world, weighing an average of 2,200 pounds. The largest mola can weigh up to 5,000 pounds and grow to be 14 feet tall and 10 feet long.
The mola live in tropical and temperate waters around the world and feed on jellyfish and small fish.
Flamingo Tongue Snail
The flamingo tongue snail's bright, giraffe-like pattern often tricks amateur shell collectors into thinking they've found a colorful shell. In fact, the shell is really white; it's the snail itself that has the striking design. The snail spreads its mantle tissue over the shell, giving it the funky look. When threatened, it recedes into the shell. The flamingo lives on Caribbean and Atlantic coral reefs at a maximum depth of 100 feet.
The giant isopod is the biggest member of the isopod family, close relatives of crabs and shrimp. Bathynomus giganteus are 14 inches long on average and weigh around 4 pounds , but one was caught in 2010 that was an astonishing 2.5 feet. They live in the deep sea between 550 and 7,000 feet and are carnivorous scavengers, feeding on dead whales, fish and squid.
They may not look appetizing, but diners in Taiwan apparently eat the giant isopod the way we feast on lobsters or crabs.
Venus Flytrap Anemone
The Venus flytrap anemone looks far more menacing than it is. Named for the carnivorous plant it resembles, the anemone uses its tentacles to catch prey and releases bioluminescent slime when disturbed. It is found mostly in the North Atlantic and can grow up to a foot wide.
Portuguese Man O' War
The Portuguese man o' war resembles a jellyfish, but it's actually a colony of interdependent organisms called zooids. The man o' war lives on the surface of the ocean, kept afloat by a gas-filled bladder. Below the bladder are tentacles extending an average of 30 feet. These tentacles are covered in venom-filled cells that paralyze and kill small fish and plankton. Although the sting is excruciatingly painful for humans, it's rarely fatal.
Man o' war are sometimes found in groups of more than 1,000 floating on the surface of warm seas. They can't independently propel themselves through water, so they either drift with currents or use their gas bladders like sails in the wind.
The flapjack octopus has been found throughout the Pacific Ocean, from Japan to Southern California. The creature was made famous by the character Pearl in Disney's Finding Nemo. Although Pearl frolics with Nemo on the coral reef, real flapjacks live in depths up to 2,000 feet.
Goosefish, also known as monkfish, are a family of angler fish found in the depths of the Arctic, Atlantic, Indian and Pacific Oceans. They have flat, broad heads with huge mouths and can grow up to 6 feet long and weigh up to 75 pounds. Their pectoral fins resemble small arms and help them move across the sea floor.
Bottom-feeders with huge appetites, goosefish have a long spine ray resembling a fishing rod, which they use to lure their prey.
The yeti crab is less than 6 inches long, but the silky hair-like structures on its claws give it a furry look similar to the mythical Bigfoot. Kiwa hirsuta was discovered in the South Pacific in 2005 living near hydrothermal vents in the seafloor.
The fibers along its legs help the yeti crab trap bacteria. While some scientists believe it uses this bacteria for food, other suspect the bacteria protects the crab from toxic minerals spewed from the hydrothermal vents.
Next: The World's Freakiest Bugs
This blood-red jellyfish known as Crossota norvegica is found more than 3,000 feet deep in the Arctic Sea. It has a deep crimson medusa (bell-shaped body) and 275 tentacles. Although it's an attention-grabbing creature, the crossota is tiny -- generally less than an inch long.