Pentecopterus, the oldest described eurypterid (sea scorpion). It’s named after an ancient Greek warship called the penteconter, apparently due to similarities in shape and “predatory behavior”, which is not a phrase I’d generally associate with a warship but fine, biologists, I’ll let it slide.
Pentecopterus could be up to 6 ft long, making it one of the largest arthropods ever, just edged out by our old friend Jaekelopterus. From the Ordovician.










