The Parastylonuridae are a family of

eurypterid Eurypterids, often informally called sea scorpions, are a group of extinct marine arthropods that form the Order (biology), order Eurypterida. The earliest known eurypterids date to the Darriwilian stage of the Ordovician period, 467.3 Myr, mil ...

s, an extinct group of

chelicerate The subphylum Chelicerata (from Neo-Latin, , ) constitutes one of the major subdivisions of the phylum Arthropoda. Chelicerates include the sea spiders, horseshoe crabs, and arachnids (including harvestmen, scorpions, spiders, solifuges, ticks ...

arthropod Arthropods ( ) are invertebrates in the phylum Arthropoda. They possess an arthropod exoskeleton, exoskeleton with a cuticle made of chitin, often Mineralization (biology), mineralised with calcium carbonate, a body with differentiated (Metam ...

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

Stylonuroidea Stylonuroidea is an extinct superfamily of eurypterids, an extinct group of chelicerate arthropods commonly known as "sea scorpions". It is one of four superfamilies classified as part of the suborder Stylonurina. Stylonuroidea, which lived from ...

(along with

Stylonuridae Stylonuridae is 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 Parastylonuridae), which in turn is on ...

), 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 ...

Description

Parastylonurids are stylonuroids with a posterior second order opisthosomal differentiation and with spiniferous appendages II-IV akin to the genus ''

Hughmilleria ''Hughmilleria'' is a genus of eurypterid, an extinct group of aquatic arthropods. Fossils of ''Hughmilleria'' have been discovered in deposits of the Silurian age in China and the United States. Classified as part of the basal family Hughmille ...

'' and non-spiniferous appendages V-VI akin to the genus ''

Parastylonurus ''Parastylonurus'' is a genus of prehistoric eurypterid. It is classified within the Parastylonuridae family and contains three species, ''P. hendersoni'' and ''P. ornatus'' from the Silurian of Scotland and ''P. sigmoidalis'' from the Silurian ...

'' or ''

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. symondsii' ...

''. Unlike the close relatives in the Stylonuridae, there are no adaptations towards sweep-feeding within the Parastylonuridae. They retain primitive ''Hughmilleria''-like prosomal appendages II-IV unsuited for such a lifestyle, and they were likely

scavenger Scavengers are animals that consume Corpse decomposition, dead organisms that have died from causes other than predation or have been killed by other predators. While scavenging generally refers to carnivores feeding on carrion, it is also a he ...

s instead of sweep-feeders.

Systematics and genera

The Stylonuridae is classified within the superfamily

within the

. The family Parastylonuridae as defined by Lamsdell et al. (2010) is paraphyletic, and knowingly made so, but was retained as it is due to the lack of complete material of either genus included within it, ''

'' and ''

Stylonurella ''Stylonurella'' is a genus of prehistoric eurypterid. It is classified within the Parastylonuridae family and contains three species, ''S. arnoldi'' and ''S. beecheri'' from the Devonian of Pennsylvania, United States and ''S. spinipes'' from t ...

''. Family Parastylonuridae Waterston, 1979 * ''

'' Kjellesvig-Waering, 1966 * ''

'' Kjellesvig-Waering, 1966

References

Stylonuroidea Silurian first appearances Silurian extinctions Prehistoric arthropod families {{Eurypterid-stub