The Portuguese man-of-war, or "sailing jellyfish," isn't a jellyfish at all — it's something called a siphonophore, and it's not an "it," but actually a "they." The man-of-war is actually a colony of four organisms, or polyps, that make up four different body parts: a top gas-filled bladder, the feeding tentacles, the prey tentacles, and the reproductive polyp. The top polyp, the gas bladder, is actually used to sail through the wind, the creature's only means of transport other than drifting on ocean currents.
Nudibranchs are soft-bodied mollusks, much like your average slug — but flashier. They're known for their dazzling array of colors and textures. Many feed on toxic sea animals, such as corals and anemones, and some are able to use the poisons they ingest to become toxic themselves.
The flamingo tongue snail is a common fixture on Caribbean coral reefs, as well as in the Western Atlantic and the Gulf of Mexico. It lives and feeds on gorgonians, also known as sea fans or sea whips and is able to absorb their toxins to become toxic, itself. The snail's bright orange and pink outsides are actually a fleshy covering over its white shell.
The blob sculpin's oddly expressive face makes it look like it could jump right out of the water and start a conversation — but, in fact, it’s a pretty shy customer. The sculpin hangs out in dark, deep-sea waters, munching on small invertebrates like crabs and mollusks. It can grow up to two feet in length.
The glass squid, also called the cockatoo squid, is one of the stranger deep-sea creatures, with its transparent, balloon-shaped body and giant eyes. Many species are also capable of bioluminescence using special light-producing organs.
These Christmas tree worms present a festive image. They're a kind of polychaete, or marine worm, and they come in a variety of bright colors. Their spiraling appendages help them catch tasty phytoplankton out of the water to eat.
Giant tubeworms are found in the ocean's most inhospitable spots. They thrive near hydrothermal vents on the ocean floor, which spew boiling water and toxic gases.
This "supergiant" amphipod looks kind of like a shrimp, except way bigger. Like the shrimp, the amphipod is a crustacean. Most only grow to be a a few millimeters long, but several years ago a group of researchers captured this gigantic specimen, along with a handful of other "supergiant" amphipods. The largest known amphipod on record grew to be about a foot long.
This ghostly tube is a colony of composed of dozens of tiny animals called tunicates, or "sea salps,", all feeding and moving as a single mass. Colonies can grow to be 15 feet long, move by jetting water through their bodies, and are capable of producing light through chemical reactions in their bodies.
The goblin shark is rarely seen underwater, but a few have recently been brought up in fishermen's nets on land. It is known for its strange long snout, which is used for digging in the sand. It has pink coloring, bluish fins, a flat head, and a protruding jaw. The shark uses its needle-like teeth like claws.
This cookiecutter shark may only be about the size of a house cat, but it packs a nasty punch. It gets name from its bizarre, round bite — it leaves its victims looking as though someone attacked them with an ice cream scoop. The key is the circular sawing motion the shark uses to gnaw off lumps of flesh.
The basket star is a kind of brittle star, an animal closely related to sea stars. It sets itself apart from the other brittle stars with its bizarre mass of branching legs, which are full of little hooks used for grabbing and holding on to prey.
Leafy seadragons have some of the most elaborate camouflage of any animal in the sea. Their delicate, leafy appendages allow them to blend seamlessly in with surrounding seaweed.
The starfish in the photo looks like it's resting on top of a rock or maybe a coral. But that colorless lump is actually a xenophyophore, the largest single-celled organism in the world. Xenophyophores can grow to be about 10 centimeters long. They are found only in the deep sea.
The viperfish is best known for its intimidating bite — those needle-like teeth are so big they don't even fit inside the fish's mouth when it closes its jaws. The viperfish primarily sticks to the deep sea and uses a light-producing organ on its back to lure in its prey.
The frogfish is a master of camouflage, as you can see from this photo. They make up a family of fish often referred to as "anglerfish," and some are even capable of changing colors.
The Sargasso Sea is actually an ocean-locked patch of sea located within the Atlantic. Its boundaries are defined by four different ocean currents, and are therefore always changing. The sea is named after a vagabond algae that inhabits its waters and lives its entire life without ever making port on solid ground (you can see a few patches of it in this photo). The sea provides important habitat for many creatures including sharks, eels, and even humpbacks.
The frilled shark looks more like a sea monster than anything else, with its serpentine body and strange set of jaws. Its mouth is filled with row after row of needle-sharp teeth — up to 25 rows in all — and it gets its name from its frilly, fringed gills.
The mid-oceanic ridge system is the longest mountain chain the world, and it's almost entirely under water. It's made up of a series of volcanic ridges throughout the world's oceans, formed by shifting tectonic plates. Altogether, it's more than 40,000 miles long. This erupting volcano is located at the edge of the Tonga Ridge, which is just one part of the mid-oceanic ridge system.
Sea cucumbers aren't all drab and shapeless — they come in a variety of colors, designs, and textures. This stunning red-lined sea cucumber is one example, but many others, such as the Spanish dancer or pink see-through fantasia sea cucumbers, are equally as dazzling.
Noctiluca scintillans, or “Sea Sparkle,” usually shows up as an eerie, pale glow in the water. The shimmering light is caused by colonies of microscopic protists called dinoflagellates, capable of bioluminescence. Though pretty in the moonlight, it can be deadly in large quantities. Sometimes Noctiluca experiences a “bloom,” or a massive population burst, releasing large amounts of toxic ammonia into the ocean and killing off fish and other marine animals.
The sea angel is another kind of soft-bodied mollusk, so named for its ethereal, winged appearance. They swim freely through the ocean and feed on other mollusks.
A blue hole is an underwater sinkhole. This one, dubbed the "Great Blue Hole," is found off the coast of Belize and is nearly 1,000 feet in diameter.
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