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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Hyperiid amphipods are small crustaceans related to sand fleas and distantly related to shrimp. They range in size from very tiny to more than 7 inches long, and are found at all depths of...
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Bioluminescence is one of the more captivating adaptations that have evolved in...
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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Like its terrestrial namesake, the Venus fly-trap anemone ( Actinoscyphia sp.) sits quietly and waits for food to drift into its outstretched tentacles, which are lined with stinging harpoons called nematocysts. Of course, this...
Two bright orange anemonefish ( Amphiprion ocellaris ) poke their heads...
White abalones are slow-moving, algae-eating mollusks. Rapid overharvesting...

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Giant squid live up to their name: the largest giant squid ever recorded by scientists was almost 43 feet (13 meters) long,...
Found in Arctic waters, this rare deep-water species of larvacean , Oikopleura gorskyi , eats by filtering particles from the seawater it drifts through. Larvaceans build 'houses' around themselves...
Flower-like clusters of polyps make up this coral colony. Their pink color comes from the zooxanthellae living inside. More about coral reef ecosystems can be found in our Coral Reefs featured story .
This magnified photo provides a close-up look at copepods—tiny crustaceans that right whales feed on. There are many species of copepods that live throughout the water column, from floating at the...
Syllid fireworms are a part of the Syllidae family , which is a type of polychaete worm. Usually these small worms, not getting much bigger than 13 cm, live on the ocean floor. But when the worms...
With a scientific name that means "the vampire squid from hell," you'd expect the vampire squid ( Vampyroteuthis infernalis ) to be a fearsome predator terrorizing the deep. Despite its demonic look...
In 2012, the long-elusive giant squid was finally filmed live in its natural habitat. The squid was found by placing glowing lures outside of a submersible to mimic jellyfish, which typically...
What reef animal comes in a rainbow of crazy colors, can throw out its stomach to immobilize predators, then creep away and regrow a brand-new stomach? It’s the sea cucumber, prized as a gastronomic...
The European green crab ( Carcinus maenas ) has spread far beyond its native continent, to waters off North and South America, Asia and Australia. It's a voracious eater and poses a nuisance to...
Even on an early winter morning, it was sunny and warm in southern Florida. This was great because, regardless of the weather, Dr. Jon Norenburg and I were going to walk chest-deep into the water to...
In this video Smithsonian research zoologist Dr. Martha Nizinski takes viewers with her as she searches for crustaceans in the deep sea . She's particularly interested in finding squat lobsters ,...
The over 1,000 species of ribbon worms ( Nemertea ) are mostly found in marine environments (like the Hubrechtia found in a mud flat, in the photo). These worms have both a mouth and an anus (unlike...
Coral reefs are the most diverse of all marine ecosystems. They teem with life, with perhaps one quarter of all ocean species depending on reefs for food and shelter. This is a remarkable statistic...
Come one, come all! See the amazing, the astonishing, half-animal, half-plant! Journey to Tampa Bay, Florida, where scientist Skip Pierce and one of his students first made a remarkable discovery...
This bearded fireworm ( Hermodice carunculata ) must have a strong stomach -- it’s sucking on fire coral ( Millepora sp. ), which would give the unlucky snorkeler a nasty sting. Encountered in St...
Scientists describe the amazing bioluminescent creatures they encounter as they descend into the deep--siphonophores, ctenophores, and viperfish--in this Smithsonian/History Channel "Deep Ocean...
Sea stars ( Odontaster validus ) and sea urchins ( Sterechinus neumayeri ) spread over an algae-covered seafloor off the coast of Antarctica. These two species are often found living in association...
The open ocean is surprisingly barren to the naked eye. Every now and again you will encounter a school of fish and their attendant predators, but most of the life that you find is gathered around...
This brilliant red octopus ( Benthoctopus sp. ) was photographed at more than 8,800 feet (about 2,700 meters) in Alaminos Canyon in the Gulf of Mexico. See more photos of wild creatures encountered...
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