An image of a jellyfish, and an image of a giant squid. Perfect for fans of Captain Nemo and the Nautilus. A few species of jellyfish live 30,000 feet under the sea. The squid can dive over a mile deep, most of us suspect is where Jules Verne got the title 20,000 Leagues Under the Sea. But since 20,000 leagues is roughly 60,000 miles, this would be the distance the Nautilus traveled, not the depth.