Eurypterids

Eurypterids or giant sea scorpions are extinct marine arthropods that form the order Eurypterida with about 450 species that appeared either late Cambrian-early Ordovician approximately 467 million years ago and went extinct about 251 million years ago during the Permian-Triassic extinction event also known as the great dying where 90% of species went extinct the Jaekelopterus being possibly the largest arthropod which reached about 7.5-8.5ft or 2.3-2.6 meters and the smallest being  Alkenopterus which was about 0.80 inches or 2.03 centimeters they ate anything smaller than the including smaller members of the same species and they were apex predators and were capable of swimming rapidly at their prey before grabbing them with their spiny claws then ripping then into pieces they could chew and their closest living relative are horseshoe crabs