Shark with the most gill slits

The vast majority of modern-day shark species famously have just five pairs of gill slits. However, a few have six pairs, and two have seven pairs - a primitive condition hearkening back to prehistoric times. These two species are the sharpnose sevengill shark Heptranchias perlo and the broadnose sevengill shark Notorhynchus cepedianus. Fossil sharks very similar in basic form to these are known from remains dating back to the Jurassic Period, 200 million years to 145 million years ago.