Uraraneida


Uraraneida is an extinct order of arachnids, known from fossils of Middle Devonian, Permian and possibly Cretaceous age. Two genera of fossils have been definitively placed in this order: Attercopus from the Devonian of United States and Permarachne from the Permian of Russia. In 2018, a third genus Chimerarachne, from the Cretaceous of Myanmar was proposed to belong to this group, but this placement is disputed. When the first fossils were found, they were identified as spiders, but now constitute the Uraraneida, a separate but closely related group.

Characteristics

The first fossil now placed in the order was found in Gilboa, New York. In 1987, it was initially tentatively placed in the extinct order Trigonotarbida and named Gelasinotarbus? fimbriunguis. Later, partly on the basis of a supposed spinneret, it was identified as a spider and named Attercopus fimbriunguis. Further specimens of this species were found, and when examined in detail, along with those assigned to the genus Permarachne, features inconsistent with their placement as spiders were revealed. Silk producing spigots are present, but are borne along the rear edges of ventral plates, not on appendage-like spinnerets, as in spiders. The specimens also have a long, jointed "tail" or flagellum at the end of the abdomen, after the anus, a feature lacking in spiders but present in some other arachnids, such as uropygids.

Phylogeny and classification

A 2014 study placed the Uraraneida in the Tetrapulmonata, a clade of arachnids defined by the apomorphy of two pairs of book lungs. The Tetrapulmonata divide into two main clades, one of which, Serikodiastida, unites Uraraneida and Araneae, groups that share the ability to produce and use silk.
An alternative classification suggested by Wunderlich in 2015, based on the same phylogeny, makes Uraraneida a suborder of Araneae, with "true spiders" treated as suborder Araneida.
Selden et al.Wunderlich
clade Serikodiastida
  • order Uraraneida
  • order Araneae
order Araneae
  • suborder Uraraneida
  • suborder Araneida
    • In 2016, a fossil arachnid from the Pennsylvanian age was described under the name Idmonarachne brasieri. It resembles uraraneids in lacking spinnerets, but unlike them resembles spiders in lacking a flagellum. The Late Carboniferous appears to be a time when there was a greater diversity of tetrapulmonate arachnids, of which the uraraneids were just one group. In 2018, two groups simultaneously published a new taxon which was considered either closely related to or a member of the Uraraneida.

    Genera and species

    Dunlop et al. accepted two species:
    Huang et al. placed another species in this order: