Sea Squirts Have Precursor to Human Heart

Sea squirts may not get a lot of respect in the animal kingdom, but at heart, they’re really a lot like us, a new study says.

That’s because the marine invertebrates have cells that beat in a similar pattern to the human heart, scientists say. (See a picture of a carnivorous sea squirt.)


The sea squirt Botryllus schlosseri

Image courtesy USGS Nonindigenous Aquatic Species Database, Gainesville, Florida.

For their study, Annette Hellbach from the Max Planck Institute of Biochemistry in Germany and colleagues observed the tubular heart of the colonial sea squirt Botryllus schlosseri. (See colorful sea creature pictures.)

The team found that the heart’s contractions start at one end of the heart and travel across the length of the organ, then “periodically reverse, suggesting the presence of two pacemakers, one on each side,” according to the study.

Hellbach expected to find what’s called “HCN cells”—markers for pacemakers—on both ends from which the heartbeat begins, but instead found them throughout the heart.

They backed up the finding by giving the sea squirts chemicals that slow heartbeats in mice—and found the drugs also worked on the invertebrates. “This increases the likelihood that the cells operate through a similar molecular function,” according to a press statement.

Such an elaborate cardiovascular system in the sea squirt may be an early precursor to the mammalian heart, suggests the study, published July 18 in JEZ A: Ecological Genetics and Physiology.

And the modern human heart is certainly something to behold. Take a study I covered in May, which found watching a friend or relative in a stressful situation can loosely synchronize both of your heart rates, as shown via experiments at a fire walking ritual.

In the experiment, when a spectator observed a relative or friend walk across hot coals, both the onlooker and performer’s heart rates changed at the same time, though they didn’t match each other beat for beat.

And though you can’t mend a broken heart, cells are replaced over our lifetimes, a 2009 study found.

It had long been a mystery whether human adults have a set number of heart cells or whether cells are added to replace old ones over time. But the research found that heart muscle cells, which are responsible for the contractions that pump blood through our bodies, can in fact renew themselves.

Now that’s heartening news.

Check out more weird coverage on National Geographic News.


Meet the Author
Christine Dell'Amore, environment writer/editor for National Geographic News, has reported from six continents, including Antarctica. She has also written for Smithsonian magazine and the Washington Post. Christine holds a masters degree in journalism with a specialty in environmental reporting from the University of Colorado at Boulder. Her book, South Pole, was published in 2012.