Range: Marine waters worldwide Habitat: Varies by species Size: About 4 inches (10cm) in diameter Diet: Kelp, algae, plankton, mussels, decaying bodies, and more Threats: Sea stars, parrotfish, triggerfish, lobsters, foxes, and otters Life span: Up to one hundred years

Transcript:

Today on Animal Fact Files we're talking about sea urchins. The subscribe button isn't spiny, be sure to click it! Pterodactly Tyler made today's spiky request. We’ve actually previously discussed a specific kind of sea urchin, the sand dollar, but today we’re focusing on the globular, spiny guys most people call sea urchins.

Sand dollars are considered “irregular” sea urchins, while the sea urchins we’ll be talking about today are considered “regular”. As a general rule of thumb, sand dollars are flat, have super short spines, and are found in sand while other sea urchins are spherical in shape, have long spines covering their body, and live on hard substrates. They both, however, have a strong mouth with plates that act like teeth. Some sea urchins are so strong they can bore through steel.

Sea urchins are mostly nocturnal and try to avoid light whenever possible. Sometimes they’ll dig into rock formations in order to create hiding spots. It’s been observed that sea urchins who begin burrowing while young, will end up growing too big to be able to remove themselves from the holes they excavate. Technically, they can survive like this if enough food floats by, but they still can’t escape. I guess you could say they’re the ultimate hermits.

Sea urchins will eat pretty much anything edible they come across. Kelp, algae, plankton, mussels, decaying bodies - they're like marine Roombas. These echinoderms can be found in all the world’s oceans, and, though they do occur in shallow waters and tide pools, they are usually found more abundantly in colder, offshore waters sometimes reaching depths of more than three miles (4.8km).

They can grow to about four inches (10 centimeters) in diameter, not including the spines. While sea urchin spines look imposing, for the most part these creatures are harmless to humans. Just think of a sea urchin as a hedgehog of the sea - you can hold it and usually be fine, but don’t step on it; that’s bad for everybody involved.

While their spines are made to protect them from predators, sea urchins are eaten by sea stars, fish such as parrot and triggerfish, crustaceans like lobsters, and even mammals including foxes and otters. If an otter has been munching on enough sea urchins its teeth and even its bones will turn the color of its spiny meals. A deceased sea urchin is spineless - well, technically so is a live one - that’s some invertebrate humor for you. *crickets*

Sea urchins reproduce in much the same way that many creatures of the sea do: by pooing out all their reproductive stuffs and hoping for the best. This is called spawning, and depending on the species it may happen year round or during certain times of the year. Considering there are nearly 1,000 species of sea urchins, this can vary drastically, but the ultimate goal is always to successfully pass on genetic material and create a new generation.

Sea urchins eggs will develop into larvae once fertilized who may drift about the open ocean for a time before settling to the sea floor. Once settled, they’ll begin transitioning into their adult form with the formation of their test. A test is a sea urchin skeleton - it’s the part that’s left behind and sold in beach shops everywhere. Supposedly, sea urchins can live to be more than 100 years old. What do you think about that?

For more facts on sea urchins, check out the links in the description. Give a thumbs up for sea life, and thank you for watching Animal Fact Files.