All life began in the sea. Multicelled animals without backbones— the invertebrates—a rose in the oceans roughly 700 million years ago, and for upward of 200 million years, they were the only game in town. No animals lived on land, and vertebrates, in the form of fish, had yet to emerge. A menagerie of otherworldly creatures evolved during this very long stretch of time, becoming the ancestors of the marine animals we recognize today as sea anemones, starfish, snails, corals, clams, crabs, and worms. Calling them ancient doesn’t even capture the mysterious, deep history of life on our planet. Although emergence of the actual first animal is buried in deep time, all these creatures have prospered for at least 580 million years since their original forms appeared in the Precambrian era, and countless new species have evolved from each group. Plenty of time and circumstance allowed these animals to perfect staggering biological feats unlike any we see on land. There are animals that photosynthesize like plants, animals that transform wavelengths of light with engineering precision, animals that build castles of glass or limestone using seawater. There are animals that conjure really strange and powerful chemicals that we now use as drugs. I sometimes call the different processes that produce these feats “magic tricks” because, despite our best science efforts, some parts of the essential biological processes are enigmatic, controversial, or shrouded in mystery.
When spineless sea creatures emerged in the ocean over 600 million years ago, their exceptional, multicellular biology upended the balance of power that had previously prevailed beneath the waves. Before them, life in the oceans was dominated for billions of years by single- celled bacteria and protozoans. As the first larger, multicelled animals such as ancestors of jellyfish, sea anemones, and sponges emerged, they transformed the world. Like superheroes, these new animals possessed novel powers that expanded the natural world and allowed them to persist for hundreds of millennia to survive in the oceans today.
All life began in the sea.
In the words of E. O. Wilson, “The love of Nature is a form of religion, and naturalists serve as its clergy. . . . Grant nature eternity on this planet, and we as a species will gain eternity ourselves.” As a Cornell University professor teaching invertebrate biodiversity and marine ecology, and as the curator of the Blaschka invertebrate glass collection, I have been privileged to travel the world’s oceans on the hunt for some of its most unusual creatures. C. S. Lewis urges would-be writers to tackle what they know and love. Marine invertebrates are my life’s passion and somehow, it’s the very ancient and seemingly simpler ones that I find most captivating and surprising: the sponges, corals, jellyfish, and sea slugs. Although less well-known than beloved whales and dolphins, the spineless biota manages the balance of nature in the oceans through creating habitats like coral reefs, controlling the flow of energy through entire food webs, and engineering transformations that baffle scientists to this day.
The ideas animating this book began to drift in my mind many years ago, when I was in college and first fell in love with life in the sea. I became fascinated with the many shapes, body plans, and glittering colors I saw when exploring the rich tide pools of the Pacific coast, and when I did my first scuba dives. There were animals without heads, legs, or eyes. Creatures that looked more like flowers than animals. Animals that had shells and fearsome claws for protection and others that seemed completely vulnerable but were loaded with the most toxic chemicals on the planet. My fascination led me to study marine ecology in graduate school and as a professor at Cornell. The more I learned about the critters in the oceans without backbones— the corals, sponges, worms, jellyfish, clams, crabs, and octopuses that make up 99 percent of diversity in the ocean— the more awe I felt in seeing the marvelous adaptations they had for getting food, reproducing, and avoiding their killers in an environment spinning with an abundance of life. I spent thousands of hours underwater studying how spineless animals run the economy of undersea worlds, and reporting back to an audience of other scientists. A committed reader myself, I longed to share my knowledge and fascination with a broader audience.