Brachiopods are marine invertebrates belonging to the Phylum Brachiopoda, characterized by two bilaterally symmetrical valves. While many types of animals were common on the seafloor, none were more important than the brachiopods. During the Ordovician, brachiopods were the dominant shellfish; in fact, if you went to the seashore anytime from 550 to 250 million years ago, most of the shells you would have collected would be brachiopods. Only after the Permian mass extinction did the brachiopods become less important than clams in the ocean ecosystem. Although you won’t find brachiopods at the beaches off North America today, they are still in existence living in the cold waters off the coast of the Pacific northwest, Alaska, New Zealand, Antarctica and other cooler oceans of the world.