A Silurian Reef

a reef scene with fish and large "sea scorpions"
(Julius Csotonyi, Smithsonian Institution)

The eurypterids, a group of arthropods, were some of the most fearsome predators and could grow up to six feet (2 meters). With long tails that ended in a spike, they are often called "sea scorpions." Here, two species of eurypterids swim in a reef with fish.