We swam in a companionable silence for a few more minutes, stopping to examine a couple of submerged wrecks. I imagined the experience would be a lot like scuba diving, except every video I’d ever seen of humans underwater showed them as slow and ungainly, struggling to push themselves through the water at a snail’s pace. The Quinlan forms moved more like otters—or maybe penguins, since the Quinlans didn’t quite have the sinuous flexibility of otters.