Pterygotus is the secon-largest known eurypterid, or sea scorpion and one of the largest arthropods of all time. It could reach a length of 2.3 m (about 7 feet), had a pair of tremendous compound eyes, as well as another pair of smaller eyes in the center of its head, and 4 pairs of walking legs, a fifth pair modified into swimming paddles, as well as a pair of large chelae (pincers) for the subduing of prey. The foremost 6 tergites, or tail sections, contained gills and the reproductive organs of the animal.