Sea Urchin

Sea Urchin Facts
Size 1.2-4 in (3-10 cm); up to 3 inch (8 cm) (spines)
Speed Unknown
Weight Unknown
Lifespan 15-200 years
Food Algae
Predators Fish, birds, crabs, sea otters
Habitat In oceans worldwide
Phylum Echinodermata
Class Sea urchins
Scientific name Echinoidea
Characteristics Spines that can cause painful wounds

There are more than 200 species of sea urchins in all colors and shapes. They live on rocky surfaces in shallow and deeper waters in depths up to 295 ft (90 m).

Why Do Sea Urchins Have Spines?

Sea urchins are not very popular. If you have already stepped on one of them accidentally, you know why. The spines of the sea urchin can cause terrible pain. There are even sea urchins that inject poison with their spines – quite similar to a needle. Leather urchins even have venomous pedicellariae, others only short spines. The spines have the following functions:

- Defense
The spines are ideal to keep other sea creatures away. Other than the hedgehog, the sea urchin does not need to roll itself up.

- Movement
Between the spines, the sea urchin has thin tubes, which function as feet. Depending on how much water the urchin pumps into these tubes, the pressure is higher or lower. This determines how firm or soft the tubes are. If the tubes on the right side are soft, the urchin sinks to the ground on the right side and thus moves a little bit forward. For comparison: Bend your right knee. In which direction does your body move?

- Eating
Lots of food particles are floating through the water while the urchin is sitting on the ground of the ocean, so that it can catch them with its spines.

Sea Urchin Sea Urchin - Photo: NatureDiver/Shutterstock

And Where is the Mouth?

The mouth of the sea urchin sits in the centre of the bottom side of its round body and has five tooth-like plates to grind food.

When in Danger, Sea Urchins Clone Themselves

The larvae of the sand dollar sea urchin clone themselves when they feel threatened by a fish. After this there are two smaller identical animals, which are harder to detect for the enemy.

Sea Urchin Sea Urchin - Photo: Wanida Srimongkol/Shutterstock


The red sea urchin Strongylocentrotus franciscanus can get up to 200 years old.


Female sea urchins release about two millions of small eggs into the water to be fertilized by the male sea urchin. The larvae spend about 2-5 years in the plankton until they are able to move along on the ground of the ocean.

Sea Urchin Sea Urchin - Photo: almondd/Shutterstock

Sea Urchin Sea Urchin - Photo: Brandon B/Shutterstock

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