The euriptids were large arthropods that are now extinct. They can be visualised somewhat as a very large water scorpion They existed during the silurian period, and are thought to have been one of the most major aquatic predators that existed at that time.

The physical form of euriptids was quite varied, but they shared many similar features. All possesed eight legs. They had highly developed sensory organs, allowing them to accurately track prey, and large claws with which to swiftly disable them. A large, broad tail would have allowed great speed, either to chase, or to flee. The largest euriptid is thought to have been more than six feet long.

The species on which they preyed most often would have been trilobites and bony fish. These were both well armoured, but the strong claws of the euriptid could have crushed them.

One species of eurypterid, Mixopterus, even had pincers and a telson similar to terrestrial scorpions. Some scientists hypothesize that Mixopterus might have been venomous, though it's not known for certain, and would be difficult to determine from fossil evidence.

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