Sea Urchins

[denise]

Sea urchins are slow moving, spiky animals that live on the seafloor, anywhere from shallow waters to ocean trenches. There are more than 700 different species of sea urchins worldwide. Their numerous spines have many functions: they are used for protection, for movement, and for trapping drifting algae to eat. Some sea urchins have venomous spines. Amongst the spines are rows of tiny tube feet with suckers that help with movement and to hold onto the seabed. Like their cousins the sea stars and sand dollars, sea urchins do not have a brain.


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Close up of a sea urchin, showing an impressive set of spines

Despite their excellent defenses that make them as palatable as a pincushion, sea urchins still have many enemies, they are eaten by otters, wolf eels, lobsters, crabs, and even humans! In many parts of the world, sea urchins are harvested by humans and served as a delicacy.


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Long Spined Urchin on a reef in Boynton Beach

Some sea urchins use camouflage to try and avoid potential predators. Using their spines and tube feet they hold onto stones, algae or even anemones, and carry them around on their back. Others rely on symbiotic relationships with cardinalfishes and shrimpfishes for protection.



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Long spined sea urchin camouflaged amongst a coral reef, Key Largo
Picture by Courtney Redfield

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Purple Pincushion Urchin covering itself, Blue Heron Bridge
Photo by Joe Stillman

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Pencil Urchins, Pompano Beach