for National Geographic News
Sea urchins and humans have a remarkable amount in common—genetically speaking.
Scientists already knew that the creatures, which resemble underwater hedgehogs, are one of only a few invertebrates (animals without backbones) on the human branch of the evolutionary tree.
But a new sequence of the California purple urchin's genome reveals that the marine creatures and humans bear a striking number of similarities. (See related news photo: "Sea Urchin Genome Decoded".)
"Comparing all the genes of the sea urchin, it's actually quite similar to us," said George Weinstock, who led the sequencing project. Weinstock is co-director of the Human Genome Sequencing Center at Baylor College of Medicine in Houston, Texas.
The sea urchin is one of the few marine organisms whose genome has been sequenced. The study therefore also provides insights into the vital role of sea urchins in many marine ecosystems.
"Sea urchins are major grazers in shallow seas of many parts of the world's oceans ... and they are the main prey of many top predators," said John Pearse, a biologist at the University of California, Santa Cruz.
Results from the sequencing project and accompanying articles, including one by Pearse, will appear in tomorrow's issue of the journal Science.
Sea urchins, which feed mainly on algae, live in environments that alternate between species-rich kelp forests and sea urchin-dominated "barrens."
"They are known to limit sea grass and kelp production and consequently the diversity and complexity in communities supported by these producers," Pearse said.
He compares sea urchins to rabbits and other grazers found on land.
"Sea urchins are the main prey of many top predators—including crabs, lobsters, fish, and sea otters—that directly limit their abundance, comparable to how coyotes, hawks, and owls limit the abundance of rabbits," Pearse said.
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