''Plesiosiro'' is an extinct arachnid genus known exclusively from nine specimens from the Upper

Carboniferous The Carboniferous ( ) is a geologic period and system of the Paleozoic that spans 60 million years from the end of the Devonian Period million years ago ( Mya), to the beginning of the Permian Period, million years ago. The name ''Carbonifero ...

of Coseley,

Staffordshire Staffordshire (; postal abbreviation Staffs.) is a landlocked county in the West Midlands region of England. It borders Cheshire to the northwest, Derbyshire and Leicestershire to the east, Warwickshire to the southeast, the West Midlands Cou ...

, United Kingdom. The genus is monotypic, represented only by the species ''Plesiosiro madeleyi'' described by

Reginald Innes Pocock Reginald Innes Pocock F.R.S. (4 March 1863 – 9 August 1947) was a British zoologist. Pocock was born in Clifton, Bristol, the fourth son of Rev. Nicholas Pocock and Edith Prichard. He began showing interest in natural history at St. Edward ...

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 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 Cyphophthalmi is a suborder of harvestmen, colloquially known as mite harvestmen. Cyphophthalmi comprises 36 genera, and more than two hundred described species. The six families are currently grouped into three infraorders: the Boreophthalmi, Sc ...

); the most primitive group of the living harvestmen ( Opiliones). 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 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 ...

Shultz, 2007 comprising Haptopoda, Amblypygi (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 (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 consisting of two elements, a basal paturon and a fang, which suggests a position within Tetrapulmonata. Under both equal and implied weights, ''Plesisiro'' was found to be the most basal member of a clade containing Amblypygi, Schizomida, and Thelyphonida, which was sister to the clade containing Araneae and Uraraneida.

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