Stylonuroidea are an extinct superfamily of eurypterids. They were members of the subphylum Chelicerata

Chelicerata

The subphylum Chelicerata constitutes one of the major subdivisions of the phylum Arthropoda, and includes horseshoe crabs, scorpions, spiders and mites...

.

Description

Stylonuroidea, which lived from the Ordovician

Ordovician

The Ordovician is a geologic period and system, the second of six of the Paleozoic Era, and covers the time between 488.3±1.7 to 443.7±1.5 million years ago . It follows the Cambrian Period and is followed by the Silurian Period...

 to Lower Permian

Permian

The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...

 periods, were characterized by their last pair of prosomal (head) appendages, which were developed as walking legs, or less commonly developed as swimming legs with paddles formed by the expansion of the two or three penultimate joints.

Families and genera

• Class Merostomata
  Merostomata
  Merostomata is the name given to a grouping of the extinct Eurypterida and the Xiphosura . The term was originally used by James Dwight Dana to refer to Xiphosura only, but was emended by Henry Woodward to cover both groups....
  
   Dana, 1852
• Order Eurypterida Burmeister, 1843
• Superfamily Stylonuroidea Diener, 1924
• Parastylonuridae Waterston, 1979

• Parastylonurus Kjellesvig-Waering, 1966
• Stylonurella Kjellesvig-Waering, 1966
  • Stylonuridae
    Stylonuridae
    Stylonuridae are an extinct family of prehistoric eurypterids within the Superfamily Stylonuroidea.-Description:Stylonuridae, which lived from the Ordovician to Lower Permian periods, were small to very large forms with scales developing into tubercules and knobs. The prosoma exhibited variable...
    
     Diener, 1924
• Ctenopterus
  Ctenopterus
  Ctenopterus is a genus of prehistoric eurypterid of the Family Stylonuridae. It contains only one species.-Description:Stylonurids, which lived from the Ordovician to Lower Permian periods, were small to very large forms with scales developing into tubercules and knobs. The prosoma exhibited...
  
  Clarke & Ruedermann, 1912
• Laurieipterus Kjellesvig-Waering, 1966
• Pagea Waterston, 1962
• Stylonurus
  Stylonurus
  Stylonurus is a genus of prehistoric eurypterid of the Family Stylonuridae.-Description:Stylonurids, which lived from the Ordovician to Lower Permian periods, were small to very large forms with scales developing into tubercules and knobs. The prosoma exhibited variable shape, with arcuate...
  
  Page, 1856