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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

Main Characteristics

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 feet (90 meters).


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.

Sea Urchin Sea Urchin - Photo: NatureDiver/Shutterstock


Anatomy and Appearance

Why Do Sea Urchins Have 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.

Do Sea Urchins Have a 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.

Sea Urchin Sea Urchin - Photo: Wanida Srimongkol/Shutterstock

Enemies and Threats

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.

Life Exptectancy

How Old Do Sea Urchins Get?

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

Sea Urchin Sea Urchin - Photo: almondd/Shutterstock


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 two to five years in the plankton until they are able to move along on the ground of the ocean.

Animals in the Same Biome:

Sea Urchin Sea Urchin - Photo: Brandon B/Shutterstock

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