Although popularly called "sea scorpions", only the earliest eurypterids were marine; many later forms lived in brackish or fresh water, and they were not true scorpions. Some studies suggest that a dual respiratory system was present, which would have allowed for short periods of time in terrestrial environments. The name Eurypterida comes from the Ancient Greek words εὐρύς ("eurús"), meaning "broad" or "wide", and πτερόν ("pteron"), meaning "wing", referring to the pair of wide swimming appendages present in many members of the group.