Large, segmented aquatic invertebrates (closely related to scorpions) that existed from the Ordovician to the Permian

Extinct water scorpions, up to two metres in length, making them the largest arthropods that have ever lived. These were amongst the first invertebrates to move from the sea into freshwater, and possibly for brief periods onto land.

A group of extinct arthropods which were highly successful Paleozoic predators Geologic Range: Silurian to Permian