Dawson reclassified it as a eurypterid in 1871. Pterygotus is a genus of giant predatory eurypterid, a group of extinct aquatic arthropods. Acutiramus is a genus of giant predatory eurypterid, an extinct group of aquatic arthropods. The hibbertopterids are classified as part of the superfamily Mycteropoidea within the eurypterid suborder Stylonurina. Stylonurus is a genus of prehistoric eurypterid of the family Stylonuridae. His remarkable study led to the modern breakthrough on eurypterid morphology. This giant was the last known surviving eurypterid. Sizes around are common in most eurypterid groups. Megarachne is a genus of eurypterid, an extinct group of aquatic arthropods. Hibbertopterus is a genus of eurypterid, a group of extinct aquatic arthropods. Campylocephalus is a genus of eurypterid, a group of extinct aquatic arthropods. Adelophthalmus is a genus of eurypterid, an extinct group of aquatic arthropods. It is the first record of land locomotion by a eurypterid. The earliest known stylonurine eurypterid, "Brachyopterus", is also Middle Ordovician in age. "Jaekelopterus" is the largest known eurypterid and the largest known arthropod to have ever existed.