Big pinchers

Jaekelopterus rhenaniae (410.8-402.5 Ma) is the largest known species of arthropod. It's classified as a chelicerate, which also includes sea spiders, horseshoe crabs, arachnids, and various other extinct groups. They're called "sea scorpions", but they likely didn't actually live near the sea, so someone screwed up there

^ The horseshoe crabs are close extant relatives. (As a side note, I just learned that horseshoe crabs' blood (which is blue btw) is used for pharmaceutical development since it can detect toxins, and now you also have to deal with that knowledge)