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Pseudoscorpions Temporal range: 380–0 Ma PreꞒ Ꞓ O S D C P T J K Pg N Devonian to Recent
Neobisium sylvaticum
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Arthropoda
Subphylum:	Chelicerata
Class:	Arachnida
Order:	Pseudoscorpiones De Geer, 1778
Superfamilies
Chthonioidea Neobisioidea Garypoidea Cheiridioidea Feaelloidea Sternophoroidea Cheliferoidea

Pseudoscorpions, also known as false scorpions or book scorpions, are small, scorpion-like arachnids belonging to the order Pseudoscorpiones, also known as Pseudoscorpionida or Chelonethida.

Pseudoscorpions are generally beneficial to humans because they prey on clothes moth larvae, carpet beetle larvae, booklice, ants, mites, and small flies. They are common in many environments, but they are rarely noticed due to their small size. When people see pseudoscorpions, especially indoors, they often mistake them for ticks or small spiders. Pseudoscorpions often carry out phoresis, a form of commensalism in which one organism uses another for the purpose of transport.

Characteristics

Pseudoscorpions belong to the class Arachnida. They are small arachnids with a flat, pear-shaped body, and pincer-like pedipalps that resemble those of scorpions. They usually range from 2 to 8 mm (0.08 to 0.31 in) in length. The largest known species is Garypus titanius of Ascension Island at up to 12 mm (0.5 in). Range is generally smaller at an average of 3 mm (0.1 in).

A pseudoscorpion has eight legs with five to seven segments each; the number of fused segments is used to distinguish families and genera. They have two very long pedipalps with palpal chelae (pincers), which strongly resemble the pincers found on a scorpion.

The pedipalps generally consist of an immobile "hand" and mobile "finger", the latter controlled by an adductor muscle. Members of the clade Iocheirata, which contains the majority of pseudoscorpions, are venomous, with a venom gland and duct usually located in the mobile finger; the venom is used to immobilize the pseudoscorpion's prey. During digestion, pseudoscorpions exude a mildly corrosive fluid over the prey, then ingest the liquefied remains.

The abdomen, referred to as the opisthosoma, is made up of twelve segments, each protected by sclerotized plates (called tergites above and sternites below). The abdomen is short and rounded at the rear, rather than extending into a segmented tail and stinger like true scorpions. The color of the body can be yellowish-tan to dark-brown, with the paired claws often a contrasting color. They may have two, four or no eyes.

Pseudoscorpions spin silk from a gland in their jaws to make disk-shaped cocoons for mating, molting, or waiting out cold weather, but they do not have book lungs like true scorpions and the Tetrapulmonata. Instead, they breathe exclusively through tracheae, which open laterally through two pairs of spiracles on the posterior margins of the sternites of abdominal segments 3 and 4.

Behavior

The male produces a spermatophore which is attached to the substrate and is picked up by the female. Members of the Cheliferoidea (Atemnidae, Cheliferidae, Chernetidae and Withiidae) have an elaborate mating dance, which ends with the male navigating the female over his spermatophore. In Cheliferidae, the male also uses his forelegs to open the female genital operculum, and after she has mounted the packet of sperm, assisting the spermatophore's entry by pushing it into her genital opening. Females in species that possess a spermatheca (sperm storing organ) can store the sperm for a longer period of time before fertilizing the eggs, but species without the organ fertilize the eggs shortly after mating. The female carries the fertilized eggs in a brood pouch attached to her abdomen.

Between 2 and 50 young are hatched in a single brood, with more than one brood per year possible. The young go through three molts called the protonymph, deutonymph and tritonymph. The developing embryo and the protonymph, which remain attached to the mother, is nourished by a ‘milk’ produced by her ovary. Many species molt in a small, silken igloo that protects them from enemies during this vulnerable period.

After reaching adulthood they no longer molt, and will live for 2–3 years. They are active in the warm months of the year, overwintering in silken cocoons when the weather grows cold. Smaller species live in debris and humus. Some species are arboreal, while others are phagophiles, eating parasites in an example of cleaning symbiosis. Some species are phoretic, others may sometimes be found feeding on mites under the wing covers of certain beetles.

Distribution

More than 3,300 species of pseudoscorpions are recorded in more than 430 genera, with more being discovered on a regular basis. They range worldwide, even in temperate to cold regions such as Northern Ontario and above the timberline in Wyoming's Rocky Mountains in the United States and the Jenolan Caves of Australia, but have their most dense and diverse populations in the tropics and subtropics, where they spread even to island territories such as the Canary Islands, where around 25 endemic species have been found. There are also two endemic species on the Maltese Islands. Species have been found under tree bark, in leaf and pine litter, in soil, in tree hollows, under stones, in caves such as the Movile Cave, at the seashore in the intertidal zone, and within fractured rocks.

Chelifer cancroides is the species most commonly found in homes, where it is often observed in rooms with dusty books. There, the tiny animals (2.5–4.5 mm or 0.10–0.18 in) can find their food such as booklice and house dust mites. They enter homes by riding insects (phoresy) larger than themselves, or are brought in with firewood.

Evolution

The oldest known fossil pseudoscorpion, Dracochela deprehendor is known from cuticle fragments of nymphs found in the Panther Mountain Formation near Gilboa in New York, dating to the mid-Devonian, around 383 million years ago. It has all of the traits of a modern pseudoscorpion, indicating that the order evolved very early in the history of land animals. Its morphology suggests that it is more primitive than any living pseudoscorpion. As with most other arachnid orders, the pseudoscorpions have changed very little since they first appeared, retaining almost all the features of their original form. After the Devonian fossils, almost no other fossils of pseudoscorpions are known for over 250 million years until Cretaceous fossils in amber, all belonging to modern families, suggesting that the major diversification of pseudoscorpions had already taken place by this time. The only fossil from this time gap is Archaeofeaella from the Triassic of Ukraine, approximately 227 million years ago, which is suggested to be an early relative of the family Feaellidae.

Historical references

Pseudoscorpions were first described by Aristotle, who probably found them among scrolls in a library where they would have been feeding on booklice. Robert Hooke referred to a "Land-Crab" in his 1665 work Micrographia. Another reference in the 1780s, when George Adams wrote of "a lobster-insect, spied by some labouring men who were drinking their porter, and borne away by an ingenious gentleman, who brought it to my lodging."

Classification

The following taxon numbers are calculated as of the end of 2023.

• Atemnidae Kishida, 1929 (21 genera, 194 species)
• Bochicidae Chamberlin, 1930 (12 genera, 44 species)
• Cheiridiidae Hansen, 1894 (9 genera, 81 species)
• Cheliferidae Risso, 1827 (64 genera, 312 species)
• Chernetidae Menge, 1855 (120 genera, 728 species)
• Chthoniidae Daday, 1888 (54 genera, 909 species)
• Feaellidae Ellingsen, 1906 (8 genus, 37 species)
• Garypidae Simon, 1879 (11 genera, 110 species)
• Garypinidae Daday, 1888 (21 genera, 94 species)
• Geogarypidae Chamberlin, 1930 (2 genera, 81 species)
• Gymnobisiidae Beier, 1947 (4 genera, 17 species)
• Hyidae Chamberlin, 1930 (2 genera, 41 species)
• Ideoroncidae Chamberlin, 1930 (15 genera, 86 species)
• Larcidae Harvey, 1992 (1 genus, 15 species)
• Menthidae Chamberlin, 1930 (5 genera, 12 species)
• Neobisiidae Chamberlin, 1930 (34 genera, 748 species)
• Olpiidae Banks, 1895 (24 genera, 211 species)
• Parahyidae Harvey, 1992 (1 genus, 1 species)
• Pseudochiridiidae Chamberlin, 1923 (2 genera, 13 species)
• Pseudogarypidae Chamberlin, 1923 (2 genera, 12 species)
• Pseudotyrannochthoniidae Beier, 1932 (6 genera, 80 species)
• Sternophoridae Chamberlin, 1923 (3 genera, 21 species)
• Syarinidae Chamberlin, 1930 (18 genera, 125 species)
• Withiidae Chamberlin, 1931 (37 genera, 170 species)
• †Dracochelidae Schawaller, Shear & Bonamo, 1991 (1 genus, 1 species)

Cladogram

After Benavides et al., 2019, with historic taxonomic groups from Harvey (1992).

References

1. ^ Pocock, Reginald (1911). "Book-Scorpion" . In Chisholm, Hugh (ed.). Encyclopædia Britannica. Vol. 4 (11th ed.). Cambridge University Press. p. 233.
2. ^ Schembri, Patrick J.; Baldacchino, Alfred E. (2011). Ilma, Blat u Hajja: Is-Sisien tal-Ambjent Naturali Malti (in Maltese). Malta University Press. p. 66. ISBN 978-99909-44-48-8.
3. ^ Pennsylvania State University, Department: Entomological Notes: Pseudoscorpion Fact Sheet
4. M. Beier (1961). "Pseudoscorpione von der Insel Ascension" [Pseudoscorpions from Ascension Island]. Annals and Magazine of Natural History. 13th ser. (in German). 3 (34): 593–598. doi:10.1080/00222936008651063.
5. "Endemic invertebrates" (PDF). Ascension Island Conservation Centre. Archived from the original (PDF) on 2010-05-09.
6. ^ "Pseudoscorpions". Agricultural Research Council (South Africa). Archived from the original on 2012-02-22.
7. Discontinuous gas exchange in a tracheate arthropod, the pseudoscorpion Garypus californicus: occurrence, characteristics and temperature dependence
8. Pseudoscorpions of the World | Field Guide and Catalogues
9. Peter Weygoldt (1966). "Spermatophore web formation in a pseudoscorpion". Science. 153 (3744): 1647–1649. Bibcode:1966Sci...153.1647W. doi:10.1126/science.153.3744.1647. PMID 17802636. S2CID 32393067.
10. "What are pseudoscorpions? | Field Guide and Catalogues". www.museum.wa.gov.au. Retrieved 2022-04-02.
11. Heather C. Proctor (1993). "Mating biology resolves trichotomy for cheliferoid pseudoscorpions (Pseudoscorpionida, Cheliferoidea)". Journal of Arachnology. 21 (2): 156–158.
12. Arachnida - museu nacional/ufrj
13. The possible significance of spermathecae in pseudoscorpions (Arachnida)
14. Pseudoscorpions - Bug Directory - Buglife
15. Jędrzejowska, Izabela; Garbiec, Arnold (2020). "Adaptations for matrotrophy in the female reproductive system in the pseudoscorpion <SCP> Chelifer cancroides </SCP> (Chelicerata: Pseudoscorpiones, Cheliferidae)". Journal of Morphology. 281 (10): 1160–1172. doi:10.1002/jmor.21238. PMID 32808691.
16. There are more creatures that make milk-like stuff | New Scientist
17. February, 2020's species of the month: Pseudoscorpions
18. Ross Piper (2007). Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals. Greenwood Press. ISBN 9780313339226.
19. Desert Arthropods: Life History Variations
20. "Pseudoscorpions". South African National Survey of Arachnids. Archived from the original on 2012-01-07.
21. Volker Mahnert (2011). "A nature's treasury: pseudoscorpion diversity of the Canary Islands, with the description of nine new species (Pseudoscorpiones, Chthoniidae, Cheiridiidae) and new records" (PDF). Revista Ibérica de Aracnología. 19: 27–45. Archived from the original (PDF) on 2016-03-04. Retrieved 2012-09-04.
22. "Movile Cave - An Oddity Of Romania". WorldAtlas. 25 April 2017.
23. William A. Shear, Wolfgang Schawaller & Patricia M. Bonamo (1989). "Record of Palaeozoic pseudoscorpions". Nature. 342 (6242): 527–529. Bibcode:1989Natur.341..527S. doi:10.1038/341527a0. S2CID 4324620.
24. Wolfgang Schawaller, William A. Shear & Patricia M. Bonamo (1991). "The first Paleozoic pseudoscorpions (Arachnida, Pseudoscorpionida)". American Museum Novitates (3009). hdl:2246/5041.
25. Judson, Mark L. I. (March 2012). "Reinterpretation of Dracochela deprehendor (Arachnida: Pseudoscorpiones) as a stem-group pseudoscorpion: STEM-GROUP PSEUDOSCORPION". Palaeontology. 55 (2): 261–283. doi:10.1111/j.1475-4983.2012.01134.x. S2CID 129220288.
26. Schwarze, Daniel; Harms, Danilo; Hammel, Jörg U.; Kotthoff, Ulrich (2021-06-22). "The first fossils of the most basal pseudoscorpion family (Arachnida: Pseudoscorpiones: Pseudotyrannochthoniidae): evidence for major biogeographical shifts in the European paleofauna". PalZ. 96: 11–27. doi:10.1007/s12542-021-00565-8. ISSN 1867-6812. S2CID 235600702.
27. Kolesnikov, Vasiliy B.; Turbanov, Ilya S.; Eskov, Kirill Yu.; Propistsova, Evgenia A.; Bashkuev, Alexey S. (September 2022). Taylor, Paul (ed.). "First non-amber Mesozoic pseudoscorpion from Upper Triassic deposits of eastern Europe, with a description of two new fossil subfamilies (Arachnida, Pseudoscorpiones, Feaellidae)". Papers in Palaeontology. 8 (5). Bibcode:2022PPal....8E1466K. doi:10.1002/spp2.1466. ISSN 2056-2799. S2CID 253137909.
28. Adams, George (1787): Essays on the Microscope. First edition. (London: Robert Hindmarsh)
29. "Pseudoscorpiones de Geer, 1778". World Pseudoscorpiones Catalog. 2023. Retrieved 25 October 2023.
30. Gymnobisiidae (Beier, 1947) Family: Western Australian Museum
31. Benavides, Ligia R.; Cosgrove, Julia G.; Harvey, Mark S.; Giribet, Gonzalo (October 2019). "Phylogenomic interrogation resolves the backbone of the Pseudoscorpiones tree of life". Molecular Phylogenetics and Evolution. 139: 106509. Bibcode:2019MolPE.13906509B. doi:10.1016/j.ympev.2019.05.023. PMID 31132522. S2CID 167218890.

Further reading

• Mark Harvey (2011). Pseudoscorpions of the World
• Joseph C. Chamberlin (1931): The Arachnid Order Chelonethida. Stanford University Publications in Biological Science. 7(1): 1–284.
• Clarence Clayton Hoff (1958): List of the Pseudoscorpions of North America North of Mexico. American Museum Novitates. 1875. PDF
• Max Beier (1967): Pseudoscorpione vom kontinentalen Südost-Asien. Pacific Insects 9(2): 341–369. PDF
• Peter Weygoldt (1969). The biology of pseudoscorpions. Harvard University Press, Cambridge. ISBN 9780674074255.
• P. D. Gabbutt (1970): Validity of Life History Analyses of Pseudoscorpions. Journal of Natural History 4: 1–15.
• W. B. Muchmore (1982): Pseudoscorpionida. In "Synopsis and Classification of Living Organisms." Vol. 2. Parker, S.P.
• J. A. Coddington, S. F. Larcher & J. C. Cokendolpher (1990): The Systematic Status of Arachnida, Exclusive of Acari, in North America North of Mexico. In "Systematics of the North American Insects and Arachnids: Status and Needs." National Biological Survey 3. Virginia Agricultural Experiment Station, Virginia Polytechnic Institute and State University.
• Mark S. Harvey (1991): Catalogue of the Pseudoscorpionida. (edited by V . Mahnert). Manchester University Press, Manchester.

External links

• Media related to Pseudoscorpiones at Wikimedia Commons
• Data related to Pseudoscorpiones at Wikispecies
• Video of Pseudoscorpions in Ireland

• Pseudoscorpions
• Extant Devonian first appearances