''Plesiosiro'' is an extinct

arachnid Arachnida () is a class of joint-legged invertebrate animals (arthropods), in the subphylum Chelicerata. Arachnida includes, among others, spiders, scorpions, ticks, mites, pseudoscorpions, harvestmen, camel spiders, whip spiders and vinegar ...

genus known exclusively from nine specimens from the Upper Carboniferous of

Coseley Coseley ( ) is a village in the north of the Dudley Metropolitan Borough, in the English West Midlands. Part of the Black Country, it is situated approximately north of Dudley itself, on the border with Wolverhampton. Though it is a part o ...

, Staffordshire,

United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the European mainland, continental mainland. It comprises England, Scotlan ...

. The genus is monotypic, represented only by the species ''Plesiosiro madeleyi'' described by Reginald Innes Pocock in his important 1911 monograph on British Carboniferous arachnids. It is the only known member of the order Haptopoda. The original fossils have been redescribed in detail by

Alexander Petrunkevitch Alexander Ivanovitch Petrunkevitch ( Russian: Александр Иванович Петрункевич, December 22, 1875 in Plysky near Kyiv, now Ukraine – March 9, 1964 in New Haven) was an eminent Russian arachnologist of his time. ...

in 1949 and Dunlop in 1999. A supposed example from the Coal Measures of Lancashire is a misidentification.

Relationships

Relationships with other arachnids are obscure. ''Plesiosiro'' means "close to '' Siro''", which is a genus of cyphophthalmid ( Cyphophthalmi); the most primitive group of the living harvestmen (

Opiliones The Opiliones (formerly Phalangida) are an order of arachnids colloquially known as harvestmen, harvesters, harvest spiders, or daddy longlegs. , over 6,650 species of harvestmen have been discovered worldwide, although the total number of ext ...

). These harvestmen do, in some ways, resemble the reconstructed body plan of the haptopods. Revisions have confirmed that Haptopoda should be treated as a separate and independent order. A 2007 study tentatively recognised a group named Schizotarsata Shultz, 2007 comprising Haptopoda,

Amblypygi Amblypygi is an ancient order of arachnid chelicerate arthropods also known as African cave-dwelling spiders, whip spiders and tailless whip scorpions (not to be confused with whip scorpions or vinegaroons that belong to the related order Thelyph ...

(whip spiders),

Uropygi Thelyphonida is an arachnid order comprising invertebrates commonly known as whip scorpions or vinegaroons (also spelled vinegarroons and vinegarones). They are often called uropygids in the scientific community based on an alternative name for ...

(whip scorpions) and

Schizomida Schizomida (common name shorttailed whipscorpion) is an order of arachnids, generally less than in length. The order is not yet widely studied. About 300 species of schizomids have been described worldwide, most belonging to the Hubbardiidae fa ...

(schizomids), which has been recovered subsequently in a number of other phylogenies to include fossils. All share the character of a subdivided tarsus (or foot) which gives the group its name. A 2014 analysis found that ''Plesisiro'' had

chelicerae The chelicerae () are the mouthparts of the subphylum Chelicerata, an arthropod group that includes arachnids, horseshoe crabs, and sea spiders. Commonly referred to as " jaws", chelicerae may be shaped as either articulated fangs, or similarl ...

consisting of two elements, a basal paturon and a fang, which suggests a position within

Tetrapulmonata Tetrapulmonata is a non-ranked supra-ordinal clade of arachnids. It is composed of the extant orders Thelyphonida (whip scorpions), Schizomida (short-tailed whip scorpions), Amblypygi (tail-less whip scorpions) and Araneae (spiders). It is th ...

. Under both equal and implied weights, ''Plesisiro'' was found to be the most basal member of a clade containing Amblypygi, Schizomida, and

Thelyphonida Thelyphonida is an arachnid order comprising invertebrates commonly known as whip scorpions or vinegaroons (also spelled vinegarroons and vinegarones). They are often called uropygids in the scientific community based on an alternative name for ...

, which was sister to the clade containing

Araneae Spiders (order Araneae) are air-breathing arthropods that have eight legs, chelicerae with fangs generally able to inject venom, and spinnerets that extrude silk. They are the largest order of arachnids and rank seventh in total species dive ...

and

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 '' ...

Names

The order has also been called Haptopodida; the ending -ida originated when Petrunkevitch (1955) tried to standardize the endings of the arachnid orders. Haptopoda originates from Greek "''haptos''" (= tangible, subject to the sense of touch) + "''pous'', ''podos''" (= foot) and refers to its quite long front pair of legs with their subdivided tips which look as though they might have been used to 'feel' their way around in front of the animal.

References

{{Taxonbar, from=Q19129 Carboniferous arachnids Arachnid genera Carboniferous arthropods of Europe Carboniferous England Pennsylvanian first appearances Pennsylvanian extinctions Animals described in 1911 Fossil taxa described in 1911