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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Marine parasites may be small in size, but they can be present in very high numbers and put together can weigh even more than all the top predators in an estuary or bay ecosystem!...
During the summer of 1998, scientists at the Virginia Institute of Marine...
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The blanket octopus can rip a poisonous tentacle from a Portuguese man-o-war...
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Hyperiid amphipods are small crustaceans related to sand fleas and distantly...

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Census of Marine Life researchers discovered this unusual transparent sea cucumber ( Enypniastes sp.) in the Gulf of Mexico at 2,750 meters depth. It creeps forward on its tentacles pretty slowly, at around 2 centimeters per...
Smaller than the head of a pin, this arrow squid (Doryteuthis plei ) embryo...
What are corals? Corals themselves are animals. But tropical reef-building...

DIVE DEEPER

Jellyfish and comb jellies are gelatinous animals that drift through the ocean's water column around the world. They are...
A huge colony of brittlestars (likely Ophiacantha rosea ) covers the peak of a seamount in the deep ocean. What’s the attraction? Food! Their arms reach out for tiny food particles carried by the...
There are 47 different species of seahorses and 14 of those were discovered in the last eight years, including Pontoh's pygmy seahorse ( Hippocampus pontohi ), which was officially named in 2008...
Squids, octopuses and cuttlefish, such as this Australian Giant Cuttlefish ( Sepia apama ), compose just one group of animals that call seagrass beds home. Clams and worms bury themselves in the mud...
All squid species have long been thought to lay their egg clusters on the sea floor and move on. Then in 2005, scientists from the Monterey Bay Aquarium Research Institute (MBARI) observed a deep-sea...
A fan-shaped colony of red coral ( Corallium sp.) on the Davidson Seamount provides a perch for three basket stars as they feed. See more pictures of coral in our Deep-sea Corals article.
In this photo of a shallow coral reef in the Pacific there are three species of forams . On the left, Peneroplis planatus . In the center, Amphistegina lessonii . And on the right, Laevipeneroplis sp...
Scientist Martha Nizinski holds a squat lobster ( Eumunida picta ) collected at the Lophelia reefs off Cape Lookout, North Carolina. Squat lobsters are extremely abundant there and are usually found...
These baby olive ridleys ( Lepidochelys olivacea ) will eventually provide a home to crustaceans, mollusks, and other epibionts. That's according to a survey of epibionts living on mature, nesting...
Rapa whelks , native to Asia, have invaded the Chesapeake Bay and are raising concerns about economic and ecological impacts to the Bay region due to their shellfish diet. Scientists believe that...
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...
Ochre seastars ( Pisaster ochraceus ) feed on invertebrates, such as coral and shellfish, like the mussels pictured here. The starfish forces open the shell with suction disks on the underside of its...
Giant squid live up to their name: the largest giant squid ever recorded by scientists was almost 43 feet (13 meters) long, and may have weighed nearly a ton. You’d think such a huge animal would be...
A sea monster attacks a ship in an illustration for 20,000 Leagues Under the Sea by Jules Verne. The illustration is by publisher and artist Pierre-Jules Hetzel, who is most famous for his drawings...
Many jellyfish in the class Hydrozoa, such as this hydromedusa Aglantha digitale , are transparent and easily overlooked. Learn more about hydrozoan jellies and other jellyfish , and see more...
This male giant squid is on display in the Sant Ocean Hall at the Smithsonian’s National Museum of Natural History . It measures about 2.7 meters (9 feet) long and weighs a little more than 45.5...
Last week, Smithsonian research zoologists Dr. Jerry Harasewych and Dr. Martha Nizinski were in Curaçao looking for deep-sea marine gastropods and decapod crustaceans , respectively. I learned they...
Octopuses can change the texture and color of their skin to blend in with their surroundings. This day octopus ( Octopus cyanea ) has shaped itself like seagrass or some coral so hide from predators...
Octopi (Or octopuses, both are technically correct) are renowned as one of the smartest animals alive. With no bones except for their sharp beak, they can fit through almost any hole or crevice...
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