Eurypteridae, which lived during the Silurian period, were characterized by small to large exoskeletons with inconspicuous semilunar scales or curved ridges. The telson (tail) was styliform or pointed. Eurypteridae also had chelicerae (appendages in front of the mouth) that were small. Their walking legs were covered in spines. The prosoma (head) was subrectangular, with slightly curved compound eyes located relatively centrally on the dorsal surface. Genital appendages in the female were very short with lateral lobes; but long in the male with diverging distal spines.
- Class Merostomata Dana, 1852
- Order Eurypterida Burmeister, 1843
- Suborder Eurypterina Burmeister, 1843
- Superfamily Eurypteroidea Burmeister, 1843