First scientifically described sea scorpion

The first species of sea scorpion to be scientifically described and named was Eurypterus remipes, in 1825, by American zoologist James Ellsworth De Kay. Its first-known specimen had been discovered seven years earlier, in 1818, by fossil collector S. L. Mitchill in the Bertie rock formation of New York, USA, but he had wrongly interpreted its limbs as mouth barbels, so had wrongly concluded that it was a fossil catfish.

Sea scorpions or eurypterids constitute an entirely extinct lineage of arthropods that included the largest-known of all arthropods.

Their name is something of a misnomer as only the earliest species were marine, with the many later ones being brackish or freshwater species. And although they are chelicerate arthropods like true scorpions, they are only distantly related to these latter forms.

The last sea scorpions died out around 250 million years ago, during or just before the mass extinction of the Permian Period.