They are long, stringy and date back 17 million years. They are fossilized sperm from an ancient shrimp -- the oldest, and weirdest, sperm ever discovered.

The sperm was found in the limestone of a cave in Australia by researchers combing through bat bones and guano.

The ancient beast from which the sperm came was a species of tiny muscle shrimp called ostracods. What makes the sperm so unusual is that it can uncoil to a length 10 times that of the shrimp's body.

"No one knows why ostracods have giant sperm or how they originated," David Horne, of Britain's Queen Mary University of London, told USA Today

"The new evidence that they have been around for millions of years only adds to the mystery."