Unraveling the Sea Squirt

Pesky Creature's Genome Holds Secrets to Human Origins

Adult sea squirts spend their lives stuck to a rock or boat, pumping water in one hole and out another. U.S. Department of Energy Joint Genome Institute hide caption

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toggle caption U.S. Department of Energy Joint Genome Institute
Sea squirt embryo

Sea squirt tadpoles, with their primitive spinal cords, may resemble the first vertebrate animals on Earth, which appeared in the fossil record about 550 million years ago. U.S. Department of Energy Joint Genome Institute hide caption

toggle caption U.S. Department of Energy Joint Genome Institute

Scientists have decoded the genetic sequence of humans, mice, fruit flies and many germs that cause deadly diseases. Now, they've added to that list one of the most obscure creatures on the planet: the sea squirt. Its chief claim to fame is as a pest — it grows on boat hulls and pilings. But an international team of scientists has labored to read the DNA of this animal.

As NPR's Richard Harris reports, there's a good reason why researchers have focused on the sea squirt. It occupies an extraordinary place in the chain of life. It looks like the humblest of animals, maybe a sponge or a worm. Some might even confuse it with a plant. But a look at sea squirt larvae reveals a primitive spinal cord.

Strange as it sounds, the tubular creatures are essentially vertebrates without backbones. They're much more closely related to fish, birds and people than to worms, starfish or other invertebrates. Like humans, they belong to a group of animals called chordates.

In fact, scientists say a sea squirt tadpole approximates, in some ways, what an early human ancestor — the very first chordate — may have looked like some 550 million years ago.

To that end, an international consortium of scientists has sequenced the sea squirt's genome. This week, Science magazine published the group's draft of the creature's genetic code.

Led by the U.S. Department of Energy's Joint Genome Institute, consortium scientists say they've just begun to explore the possibilities in sea squirt genetics. They're confident other biologists will seize on this animal for studying vertebrate evolution, now that its genome is available.



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