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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Today’s discoveries about our planet’s biological diversity build upon the research of previous generations of scientists. The Biodiversity Heritage Library (BHL) is a digital library committed to providing free and open access to this...
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Marine parasites may be small in size, but they can be present in very high...
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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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...
Census of Marine Life researchers discovered this unusual transparent sea...
Smaller than the head of a pin, this arrow squid (Doryteuthis plei ) embryo...

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Sample the surprising diversity of deep-sea corals. See some of the ways they differ in color, shape, and size. Explore more...
This is a tree topper unlike any other! Reminiscent of a freshly made snow angel, these pteropods are actually shell-less sea snails ( Clione limacina ). Unlike the typical snail, they flap their...
A specimen from the Smithsonian’s squid collection and videos of a mystery squid helped scientists identify a new family of deep sea squid—the Magnapinnidae, known as the bigfin squids. More about...
The Endangered Species Act (ESA) was signed into law on December 28, 1973 by President Nixon. Over 2,000 species are currently on the ESA, and they are separated into "Threatened" and "Endangered"...
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 the ocean...
This image from a scanning electron micrograph magnifies the tiny teeth that cover the surface of the giant squid’s tongue-like organ, or radula . Seven rows of sharp teeth help direct tiny pieces of...
On many of the dives, Oceana's 2011 Baltic Sea expedition team saw little wildlife in the oxygen-depleted areas. But near some marine protected areas, the crew saw an array of marine life, including...
This summer, many of you have likely enjoyed feasting on crabs, be they blue, stone, or Dungeness, and a special treat will have been the big, easy morsels of claw meat. The size of this muscle is...
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...
Talk about an investment! This octopus mom protected her brood of about 160 eggs for 4.5 years for the longest ever recorded brooding time of any animal. She was first observed by scientists from the...
Male fiddler crabs, like this one collected on Moorea, wave their enlarged claw as way of signaling to other crabs, especially during mating season. Learn more about the Island of Moorea in the...
Smithsonian Zoologist Dr. Clyde Roper , the world's foremost authority on giant squid, explores the squid collection at the National Museum of Natural History. He is passionate about giant squid and...
The spiral-tufted bryozoan ( Bugula neritina ) is being studied for a potential Alzheimer's disease and cancer drug—but it's not the bryozoan that makes the chemical. The chemical, found in the...
This transparent cockatoo squid ( Leachia sp.), also known as a glass squid, lives in the depths of the ocean and has many adaptations to help it survive there. It retains ammonia solutions inside...
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...
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...
Jellyfish and comb jellies are gelatinous animals that drift through the ocean's water column around the world. They are both beautiful—the jellyfish with their pulsating bells and long, trailing...
Chrysaora melanaster , one of the largest jellyfish commonly found in the Arctic, swims underneath the Arctic ice . Its tentacles can stretch to more than 3 meters long and pack a mean sting for...
The veined octopus ( Amphioctopus marginatus ), also known as the coconut octopus, has a skill beyond other cephalopods: it hides under animal and coconut shells, dragging them along the seafloor for...
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