Gardeners can keep their earthworms. They are worthy but uncool cousins of the marvelously diverse worms that live in the sea, creatures that do work as vital as their dirt-tunneling kin—filtering and feeding an ecosystem—but with otherworldly elegance.
Pick your ocean: It's got worms in it. They are, in fact, one of the most common marine animals, a ready meal for many of the fish we eat. Rocky and sandy shores worldwide are rife with worms, but species also float in the open water and inhabit the floor of the deep sea. Some are pinhead-size, while certain ribbon worms stretch nearly 200 feet (60 meters)—the longest animals on Earth. Some filter-feed, some stalk their prey, some eat their kin, and they have evolved at least 18 different ways to reproduce, including by breaking into pieces. An especially grand assortment occurs in shallow waters off the Hawaiian Islands, including these, photographed at sea and in the lab.
The spiny ancestors of today's marine worms were among the first sea animals more than 500 million years ago. Scientists can only guess at the number of species—estimates range from 25,000 to millions. In the 18th century the pioneering naturalist Carolus Linnaeus dumped all pliable, legless invertebrates into a single category, Vermes, but since then scientists have divided worms among various branches of life's family tree. Many of the marine worms belong to the annelids, a sundry bunch of segmented, mostly bristled animals that slide between rocks or poke from tubes. Though rarely seen, Vermes, in all their extravagant forms, have found success at sea—and help make the sea a success.