Loggerhead sea turtles migrate thousands of miles through the world’s oceans, but they don’t travel solo—research shows they carry surprisingly diverse and abundant populations of tiny creatures on their shells.

A new paper published May 20 in the journal Diversity shows that loggerhead sea turtles carry an average of 34,000 individual meiofauna—tiny organisms smaller than one millimeter—on their backs. One loggerhead carried nearly 150,000 individual animals on its shell, including nematodes, crustacean larvae, and shrimp.

“There literally is a [whole] world on there,” says Jeroen Ingels, a marine ecologist at Florida State University. It’s wild to find “that kind of diversity on another organism.”

Ingels and his team discovered more than a hundred new species of meiofauna, mostly nematodes, that hadn’t