Trilobites, meaning “three-lobed”, were the first multiple celled animals with a hardened exoskeleton to exist on earth. They dominated the shallow seas of the Cambrian period 570 million years ago and steadily declined in numbers until they became extinct 350 million years later. It is believed that predators led to their demise, though their relatives, the marine arthropods, live on today. Trilobites were sea floor dwellers and could walk, swim, and burrow into the muddy sea floor. Their segmented thorax (middle body section) enabled them to roll up into a ball for protection. Collectors are especially interested in their eyes, made up of numerous lenses packed side by side.