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.
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.
US Federal List: no special status
CITES: no special status
Spines may be poisonous, but only dangerous if stepped on or handled roughly.
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.
Sea urchins graze on algae and other organisms that grow on the rocks around them, using their Aristotle's lantern.
Arbacia punctulata is a common urchin from Cape Cod to the West Indies.
Biogeographic Regions: atlantic ocean (Native )
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).
Aquatic Biomes: benthic ; reef
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.
Other Physical Features: ectothermic
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.
