Stylonuridae is a family of

eurypterid Eurypterids, often informally called sea scorpions, are a group of extinct arthropods that form the order Eurypterida. The earliest known eurypterids date to the Darriwilian stage of the Ordovician period 467.3 million years ago. The group is l ...

s, an extinct group of

chelicerate The subphylum Chelicerata (from New Latin, , ) constitutes one of the major subdivisions of the phylum Arthropoda. It contains the sea spiders, horseshoe crabs, and arachnids (including harvestmen, scorpions, spiders, solifuges, ticks, and mite ...

arthropod Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chiti ...

s commonly known as "sea scorpions". The family is one of two families contained in the superfamily Stylonuroidea (along with

Parastylonuridae The Parastylonuridae are a family of eurypterids, an extinct group of chelicerate arthropods commonly known as "sea scorpions". The family is one of two families contained in the superfamily Stylonuroidea (along with Stylonuridae), which in tu ...

), which in turn is one of four superfamilies classified as part of the suborder

Stylonurina Stylonurina is one of two suborders of eurypterids, a group of extinct arthropods commonly known as "sea scorpions". Members of the suborder are collectively and informally known as "stylonurine eurypterids" or "stylonurines". They are known from ...

. Stylonuridae, which lived from Early Silurian to the Late Devonian, were small to very large forms with scales developing into tubercules and knobs. The prosoma (head) exhibited variable shape, with arcuate compound eyes located subcentrally, or anteriorly. Their abdomens were slender. Their walking legs were long and powerful, sometimes characterized by spines. Most genera did not have swimming legs. 1955. Merostomata. ''Treatise on Invertebrate Paleontology, Part P Arthropoda 2, Chelicerata'', P: 36.

Description

Stylonurids are stylonuroids with undifferentiated opisthosoma with appendages II-IV being spiniferous akin to the genus '' Ctenopterus'', whilst appendages V-VI are non-spiniferous akin to the genus ''

Pagea ''Pagea'' is a genus of prehistoric eurypterid classified as part of the family Stylonuridae. It contains three species, all from the Devonian (Lochkovian to Pragian); ''P. plotnicki'' from Nunavut, Canada and ''P. sturrocki'' and ''P. symond ...

''. The fixed spines on appendages II-IV could have been used as dragnets to rake through the sediment, indiscriminately entangling anything within their sweeping arc. This type of sweep-feeding also occurs in the Hibbertopteroidea, though the adaptations of the hibbertopterids suggests they were more selective feeders.

Systematics and genera

The Stylonuridae is classified within the superfamily Stylonuroidea within the

. It contains five genera in total and one recognised subfamily; the Laurieipterinae containing genera '' Laurieipterus'' and '' Ctenopterus''. "Laurieipterines" are diagnosed as stylonurids with broad metastoma and an epistoma with a rostral field and were restricted to the Early Silurian. Family Stylonuridae Diener, 1924 * ''

'' Waterston, 1962 * '' Soligorskopterus'' Plax ''et al.'', 2018 * '' Stylonurus'' Page, 1856 * Subfamily Laurieipterinae Kjellesvig-Waering, 1966 **'' Ctenopterus'' Clarke & Ruedermann, 1912 ** '' Laurieipterus'' Kjellesvig-Waering, 1966

References

Stylonuroidea Ordovician first appearances Cisuralian extinctions Prehistoric arthropod families {{Eurypterid-stub