The mangrove tunicate is a mild-looking little creature. It’s a type of sea squirt. It’s only about an inch long, and it feeds by pumping seawater through its body and filtering out the goodies. It’s found in colonies in the roots of mangrove forests around the Gulf of Mexico, the Caribbean, and the Atlantic coast of the United States.

Yet this little critter is a powerful cancer fighter. Researchers have used a compound it produces to create a cancer treatment known as trabectedin. It’s used against several types of cancer—especially those in soft body tissue, such as muscles and fat.

Cancer cells find ways to defeat many types of medication. The cells repair themselves, then continue growing and dividing, forming bigger tumors.

A recent study looked at how trabectedin fights cancer. Researchers discovered that the medication “breaks” the DNA inside cancer cells. Although the cells can fix some types of breaks, these appear to be unfixable—the cancer can’t overcome the disruption. That kills the cancer cells and slows or halts their spread.

Sea squirts are surprisingly close genetic relatives to people. And they’re easy to handle and study, so they’re popular lab subjects. So scientists have used sea squirts to create other medications, including cancer treatments. One produced from a different species is used to fight skin cancer, for example. So these quiet little creatures may yield even more treatment options in the decades ahead.