Arbacia punctulatapurple-spined sea urchin

Geographic Range

Arbacia punctulata is a common urchin from Cape Cod to the West Indies.


These purple sea urchins are found most commonly on rocks and shells in somewhat deep salt water. They prefer to live on rocks or shell bottoms from the low-tide line to a water depth of about 750 feet (229 meters).

Physical Description

Purple sea urchins, like all sea urchins, are the porcupines of the sea. They have long spines in order to deter predators. Even the name, Sea Urchin, comes from the Old English term for spiny hedgehog. The Arbacia punctulata has a deep purple color all over the spines and body (test). Their body area, called a test, can grow to a diameter of 3-5 cm. This test is made up of ten fused plates that encircle the urchin. Each of these fused plates has small holes from which the feet extend. These feet are controlled by an internal water vascular system. This sytem works by varing the amount of water inside which regulates if the feet are extended or contracted. Sea urchins also have a unique structure called Aristotle's lantern. This structure is made of five hard plates that move together like a beak. They use this beak like structure to scrape rocks clean of algae. These 'teeth' can also grow back after too much wear. They have a mouth at the underside and an anus at the top of the animal. In addition, they are radially symmetrical.


There are male and female purple urchins. The females can release as many as several million eggs at a time. These eggs settle and the sperm released from the males swims and finds the eggs, fertilizes them and creates a large gamete. The larvae that hatches is bilaterally symmetrical, and changes to radial symmetry after it grows.


Purple sea urchins move on their tube feet and spines. They are able to speed up by creating a small suction at the end of their feet by pulling water out through an opening called a madroporite. They are able to regrow broken off spines. When not feeding, theyhide in holes in worn rocks or under shells. They have been observed, to even dig their own holes and wear away at the rocks until they are worn enough to be 'comfortable' and then they will reside in that hole until the current changes or they move.

Food Habits

Sea urchins graze on algae and other organisms that grow on the rocks around them, using their Aristotle's lantern.

Economic Importance for Humans: Positive

Almost all sea urchin species are harvested for food and for their shells. Their eggs are a delicacy in many countries. They are also common laboratory species used for studying reproduction and development.

Economic Importance for Humans: Negative

Spines may be poisonous, but only dangerous if stepped on or handled roughly.

Conservation Status

The purple sea urchin, Arbacia punctulata, has been thriving in waters across the world for years and hopefully will continue to. At this time their main enemy is pollution.

Other Comments

Sea urchin studies provided the first evidence of actin in non-muscle cells.

The purple sea urchin has a symbiotic relationship with small grooming organisms that live between their spines. At first they were thought to be parasites, feeding off of the food floating by the urchin. But it was later found that they were an integral part of the animal's care by keeping the surface free from other animal or plant organisms that may have been harmfull.

For many years, Dr. William Speck, Chairman and Director of the Department of Pediatrics of Case Western Reserve University and Rainbow Babies and Children's Hospital in Cleveland, has been doing research on the causes of birth defects, using sea urchins as model organisms. He has studied various other topics all using Arbacia punctulata as his primary subject. His studies range from the effects of ethanol as a model for fetal alcohol syndrome to the effects of anticonvulsant drugs on urchins as a model for new research and development of phenytoin derivatives.


Stephanie Braccini (author), Southwestern University, Stephanie Fabritius (editor), Southwestern University.


Atlantic Ocean

the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.

World Map


Referring to an animal that lives on or near the bottom of a body of water. Also an aquatic biome consisting of the ocean bottom below the pelagic and coastal zones. Bottom habitats in the very deepest oceans (below 9000 m) are sometimes referred to as the abyssal zone. see also oceanic vent.


animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

native range

the area in which the animal is naturally found, the region in which it is endemic.


structure produced by the calcium carbonate skeletons of coral polyps (Class Anthozoa). Coral reefs are found in warm, shallow oceans with low nutrient availability. They form the basis for rich communities of other invertebrates, plants, fish, and protists. The polyps live only on the reef surface. Because they depend on symbiotic photosynthetic algae, zooxanthellae, they cannot live where light does not penetrate.


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Marine Biological Laboratory, Oct 6 1985. MBL Pediatrician Studies Birth Defects. The Collecting Net, Vol. 3 No. 6: 336-338.

Marine Biological Laboratory, 1996. Specimens - Sea Urchins. The Collecting Net, November: 12-14.

Vodopich, D., R. Moore. 1999. Biology Labratory Manual. Boston: McGraw Hill.

Wright, J. 1994. Atlantic Purple Sea Urchin. New Jersey SCUBA Diving, July: 12.