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Watch as barnacles feed on bioluminescent dinoflagellates. Barnacles are crustaceans (like crabs, shrimps and lobsters) that secrete their shells for protection while living attached to things like rocks, harbors or boat hulls. They feed...
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Depending on whom you talk to, jellyfish are either fascinating, a nuisance, a...
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The ocean is home to a phenomenal diversity of marine organisms. They have...
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This summer, many of you have likely enjoyed feasting on crabs, be they blue,...

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Zombie worms ( Osedax roseus ) eat away at the bones of a dead whale that has fallen to the seafloor in Sagami Bay, Japan. These bizarre worms rely on whale bones for energy and are what scientists call “sexually dimorphic”—the...
What are corals? Corals themselves are animals. But tropical reef-building...
In recent years, blooms of jellyfish, such as these moon jellies ( Aurita...

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Nudibranchs are a kind of sea slug, and their 3000 species are found from the poles to the tropics in both shallow and deep...
A male mudflat fiddler crab ( Uca rapax ) waves its huge claw to impress females and threaten competitors. Only the males have the large claw. When the tide is high, fiddler crabs retreat to their...
Atolla tenella , a midwater scyphomedusa , as seen under a microscope. View the “Under Arctic Ice” photo essay to learn more.
Depending on whom you talk to, jellyfish are either fascinating, a nuisance, a toxic menace, or some combination of the above. Jellyfish plop into the media spotlight when their presence causes beach...
This photo shows just a small part of the cephalopod collection at the Smithsonian's National Museum of Natural History. Shown here is Dr. Clyde Roper , a zoologist and squid expert. More about the...
In 1874, Reverend Moses Harvey of Newfoundland bought a dead giant squid caught by fishermen. More about the giant squid can be found in our Giant Squid featured story .
Some of the most otherworldly animals—like those straight from a science fiction story—can be seen in the open ocean at night. By drifting in the blackwater in a scuba suit just under the surface,...
Acorn barnacles ( Balanus crenatus ) make a home on the carapace of an edible crab ( Cancer pagurus ). Much of the Baltic suffers from eutrophication that leads to oxygen depletion. The algae blooms...
These two nautiluses ( Nautilus belauensis ) are pictured off the coast of Palau in the Pacific Ocean. There are six living species of nautilus who live in chambered shells. As they get bigger, they...
These corals from the Smithsonian collections are Stephanocyathus (A.) spiniger , a solitary, deep-water stony coral species. Around 74% of all deep-water corals are solitary, living as individual...
Stinging cells (nematocysts) line the tentacles of this moon jelly ( Aurelia aurita ). Upon contact with prey or a predator, a venom-laden harpoon shoots out to stun or kill. Read more about...
This is another view of Phromina from the side. The eyes take up most of the head, with one pair looking to the side (the red spot) and one pair facing upwards. Phronima live anywhere from 200-1100...
Dead man’s fingers ( Alcyonium digitatum ) are soft corals named for their appendage-like appearance when thrown ashore by storms. The finger-like clumps of coral polyps come in various shades of...
About 100 million years ago , during the heyday of the dinosaurs, reefs were built by mollusks called rudist clams. Like modern clams, rudists were bivalves , with two shells (or valves) joined at a...
Giant anemone. More about mangrove ecosystems can be found in the Mangroves section .
How long have jellyfish lived in the ocean? This jellyfish fossil is from the Cambrian period, more than 500 million years ago. It was found buried in Utah —an area that used to be underwater,...
It's a pygmy seahorse ( Hippocampus bargibanti ), found in Indonesia's biodiverse Coral Triangle and one of the smallest seahorse species in the world! They can change colors like a chameleon to...
Scientists have been studying why populations of crown-of-thorns sea stars ( Acanthaster planci ) have mushroomed in recent decades. Coral reefs can suffer when the sea star's numbers explode because...
The shrimp shown in this picture is a lot smaller then it looks- most adult anemone shrimp will only grow to about ½-1 inches long. Anemone shrimp ( Periclimenes inornatus ), reside as the name...
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