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Plesiosiro Temporal range: Upper Carboniferous PreꞒ Ꞓ O S D C P T J K Pg N
CT scan
Life restoration
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Arthropoda
Subphylum:	Chelicerata
Class:	Arachnida
Clade:	Tetrapulmonata
Order:	†Haptopoda Pocock, 1911
Genus:	†Plesiosiro Pocock, 1911
Species:	†P. madeleyi
Binomial name
†Plesiosiro madeleyi Pocock, 1911

Plesiosiro is an extinct arachnid genus known exclusively from nine specimens from the Upper Carboniferous of Coseley, Staffordshire, United Kingdom. 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 in 1949 and Dunlop in 1999. A supposed example from the Coal Measures of Lancashire is a misidentification.

Relationships

Plesiosiro means "close to Siro", which is a genus of cyphophthalmid (Cyphophthalmi); 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 Shultz, 2007 comprising Haptopoda, Amblypygi (whip spiders), Uropygi (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 Plesiosiro 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 Uropygi (Thelyphonida s.s.), 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

1. ^ Garwood, Russell J.; Dunlop, Jason (2014). "Three-dimensional reconstruction and the phylogeny of extinct chelicerate orders". PeerJ. 2: e641. doi:10.7717/peerj.641. ISSN 2167-8359. PMC 4232842. PMID 25405073.
2. ^ Dunlop, Jason A. (2011). "A redescription of the Carboniferous arachnid Plesiosiro madeleyi Pocock, 1911 (Arachnida: Haptopoda)". Transactions of the Royal Society of Edinburgh: Earth Sciences. 90 (1): 29–47. doi:10.1017/S0263593300002492. ISSN 0263-5933.
3. Reginald Innes Pocock (1911). A Monograph of the Terrestrial Carboniferous Arachnida of Great Britain. Monographs of the Palaeontographical Society, London. pp. 1–84.
4. Alexander Petrunkevitch (1949). "A study of Palaeozoic Arachnida". Transactions of the Connecticut Academy of Arts and Sciences. 37: 69–315.
5. Jeffrey W. Shultz (2007). "A phylogenetic analysis of the arachnid orders based on morphological characters" (PDF). Zoological Journal of the Linnean Society. 150 (2): 221–265. doi:10.1111/j.1096-3642.2007.00284.x.
6. Wang, Bo; Dunlop, Jason A.; Selden, Paul A.; Garwood, Russell J.; Shear, William A.; Müller, Patrick; Lei, Xiaojie (2018). "Cretaceous arachnid Chimerarachne yingi gen. et sp. nov. illuminates spider origins". Nature Ecology & Evolution. 2 (4): 614–622. Bibcode:2018NatEE...2..614W. doi:10.1038/s41559-017-0449-3. ISSN 2397-334X. PMID 29403075. S2CID 4239867.
7. Garwood, Russell J.; Dunlop, Jason A.; Knecht, Brian J.; Hegna, Thomas A. (2017). "The phylogeny of fossil whip spiders". BMC Evolutionary Biology. 17 (1): 105. Bibcode:2017BMCEE..17..105G. doi:10.1186/s12862-017-0931-1. ISSN 1471-2148. PMC 5399839. PMID 28431496.
8. Garwood, Russell J.; Dunlop, Jason A.; Selden, Paul A.; Spencer, Alan R. T.; Atwood, Robert C.; Vo, Nghia T.; Drakopoulos, Michael (2016). "Almost a spider: a 305-million-year-old fossil arachnid and spider origins". Proceedings of the Royal Society B: Biological Sciences. 283 (1827): 20160125. doi:10.1098/rspb.2016.0125. ISSN 0962-8452. PMC 4822468. PMID 27030415.
9. Alexander Petrunkevitch (1955). "Arachnida". In R. C. Moore (ed.). Part P, Arthropoda 2. Treatise on Invertebrate Paleontology. Lawrence: Geological Society of America and University of Kansas Press. pp. 42–162.

• Carboniferous arachnids
• Prehistoric arachnid genera
• Carboniferous arthropods of Europe
• Carboniferous England
• Pennsylvanian first appearances
• Pennsylvanian extinctions
• Fossil taxa described in 1911