Maybe it is because they look like alien beings from another world, but I have always loved watching marine life like octopuses with their stretchy, squishy bodies; dainty seahorses covered with bony plates; and translucent jellyfish that propel themselves through the water by contracting their umbrella-shaped bells. In National Geographic’s forthcoming book, Octopus, Seahorse, Jellyfish, we get up close and personal with these amazing creatures.