Invertebrates

Animals without backbones make up a huge percentage of the ocean’s biodiversity. They aren’t just small (like pteropods) or squishy (like jellyfish); the giant squid and corals that build huge reefs are also invertebrates.

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Bioluminescence is one of the more captivating adaptations that have evolved in marine animals. It's the ability of organisms to create and emit light. Dive underwater and you may witness lightshows of red, green,...
Octopuses are colorblind, but manage to blend into the background seamlessly—or...
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Fever. Aching muscles. Coughing. Sniffling. It’s flu season . Have you had your...
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The open ocean is surprisingly barren to the naked eye. Every now and again you...

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Two bright orange anemonefish ( Amphiprion ocellaris ) poke their heads between anemone tentacles. Anemonefish are able to swim amongst the stinging tentacles without getting stung — but no one knows exactly sure how. One...
White abalones are slow-moving, algae-eating mollusks. Rapid overharvesting...
This forest of Christmas tree worms is a group of polychaete worms that live...

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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...
The long silver tool shown here is a piece of traditional Australian fishing gear called a “yabbie pump.” Researchers use the device to collect burrowing shrimp and other fast-moving animals from the...
Dr. Clyde Roper prepares to dive thousands of feet to a giant squid habitat off the coast of New Zealand in a one-person submersible. More about the giant squid can be found in our Giant Squid...
Bottom trawl treasures from the shallow Chukchi Seafloor near the Canada Basin: sea stars , brittle stars , clams, some snails and crabs. View the “Under Arctic Ice ” photo essay to learn more.
You are not alone if you don’t know what forams (short for foraminifera) are, so let’s start with the basics. Simply put, forams are single-celled organisms related to the familiar amoeba that...
The mauve stinger’s ( Pelagia noctiluca ) name in German means “night light,” referring to the jelly’s reddish coloring and its bioluminescence, the display of light by a living creature. Unlike a...
This hyperiid (in the genus Cystisoma) has only one pair of eyes—but they are very big. You can see them here as the entire surface of its head and the convex orange sheet of retinal cells in the...
Researchers use Autonomous Reef Monitoring Structures (ARMS) like this one to study the diversity of coral reef organisms. They leave the structures underwater for about a year. Then they retrieve...
Dr. Clyde Roper, Smithsonian zoologist and squid expert, tries to measure up to a giant squid specimen (Architeuthis) from New Zealand. The squid wins. More about the giant squid can be found in our...
Recent scientific discoveries have revealed an underwater community of marine animals and other organisms that thrive in the dark depths of the ocean near hydrothermal vents and undersea volcanoes...
Last September, the Citizens of the Sea blog series brought you a story of doom and gloom from the reefs of Bocas del Toro, Panama. That is the time of year we typically study -- and celebrate -- the...
Researchers in Moorea use a variety of tools to collect organisms. Some are simple, everyday items like buckets and brushes, and some are…a little stranger. Here, two researchers use a “yabbie pump”...
"Harlequin shrimp normally live in pairs and their main diet is starfish... It takes a good eye and patience to find this beautiful shrimp, which looks like candy.” -- Nature's Best photographer,...
This tiny, shrimplike creature is no more than 2.5 centimeters (1 inch) long, but it’s as ferocious as a shark. Its giant eyes spot prey. Huge claws grab the prey, and a tiny mouth rips it to shreds...
These large jellyfish ( Chrysaora fuscescens ) are most commonly found along the coasts of California and Oregon. (They're also popular in the displays of public aquaria.) Their bells can grow to a...
Amidst the bright blue tufts and the dark blue fringes of the beautiful Risbecia tryoni , you might not even notice the red emperor shrimp. The two animals are native to the Indo-Pacific region, and...
The dark seafloor beneath the ice is covered with sea stars, urchins and ribbon worms looking for their next meal, which can come from sponges, dead animals that float to the sea floor, or even other...
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...
This 200-year-old bamboo coral colony is growing on the Davidson Seamount off the coast of California. The skeleton of this deep-sea coral has bamboo-like segments. See more pictures of coral in our...
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