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Brief Summary

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The Pseudoscorpiones is a group of more than 3000 known species of small arachnids that bear a pair of chelate (claw-like) pedipalps, a pair of two-segmented chelicerae, four pairs of legs, and an ovate abdomen. Pseudoscorpions superficially resemble small scorpions, but they lack the elongate tail (metasoma) and sting. The pseudoscorpions are believed to be most closely related to the sun spiders (Solifugae), with which they share many morphological similarities. (Harvey 2011) Pseudoscorpions can be found in virtually all terrestrial habitats, but are most common in leaf litter, in soil, and under the bark of trees and logs. They are frequently found in caves and many species occur along seashores. They are generally quite small, with adults ranging from around 0.5 to 5 mm in length; however, some species may exceed 1 cm. Pseudoscorpions are typically free-living, solitary predators of other tiny invertebrates. Many pseudoscorpions have venom glands within the pedipalpal fingers, making them the only venom-producing arachnids other than spiders and scorpions. (Murienne et al. 2008 and references therein) Pseudoscorpions transfer sperm in packages attached to a spermatophore, which is produced from the male’s gonopore and attached to the substrate. Males of most pseudoscorpion families that have been studied simply deposit a spermatophore without any courtship -- and even without the presence of a female. A female subsequently somehow finds the spermatophore and draws the sperm packet into her gonopore. Serianus males deposit a spermatophore in the presence of a female, but there is no physical contact between the sexes. In one branch of the pseudoscorpion family tree, however, there is an elaborate mating dance in which males actively court females, touching and moving them and culminating with the male grasping the female with his pedipalps and depositing a spermatophore on the substrate, then guiding her over the spermatophore, which she draws into her gonopore. (Harvey 2011) Pseudoscorpion eggs mature internally and the embryos are deposited into a brood-sac attached to the gonopore. The embryos mature until the protonymphs emerge from the brood-sac. They remain with the female for a short time and eventually disperse for a solitary existence.There are four post-embryonic stages: protonymph, deutonymph, tritonymph and adult. The nymphal stages are generally free-living, although the protonymphs of some species are immobile. Many pseudoscorpions build a small silken chamber in which to moult, develop their brood-sac, or shelter themselves. (Harvey 2011) Del-Claro and Tizo-Pedroso (2009) reviewed the occurrence of sociality in pseudoscorpions (extended parental care, division of labor, cooperative breeding and feeding). Individuals of some pseudoscorpion species may use their pedipalps to attach themselves to other organisms such as other arachnids, insects, mammals, or birds, which may facilitate transport to different habitats. Some are obligate commensals (i.e., benefiting from their association without harming the host, as a parasite would), spending their entire life cycle, for example, in the nests or fur of mammals (e.g. many species of Lasiochernes and Megachernes). Others form associations with flying insects, attaching themselves to legs, other body parts or, sometimes, under the elytra of beetles. Dozens of species have been collected from birds' nests (Turienzo et al. 2010). (Murienne et al. 2008 and references therein; Harvey 2011) In addition to the authoritative Pseudoscorpions of the World website, some regions have excellent online resources available for those interested in learning more about pseudoscorpions. Examples of valuable online resources include The Pseudoscorpions of Northern and Central Europe, The UK (and Ireland) Pseudoscorpion Recording Scheme, and Photographic Key to the Pseudoscorpions of Canada and the Adjacent USA.
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Pseudoscorpion

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A pseudoscorpion, also known as a false scorpion or book scorpion, is an arachnid belonging to the order Pseudoscorpiones, also known as Pseudoscorpionida or Chelonethida.

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

Characteristics

Pseudoscorpions belong to the arachnida class.[1] They are small arachnids with a flat, pear-shaped body and pincers that resemble those of scorpions. They usually range from 2 to 8 millimetres (0.08 to 0.31 in) in length.[2] The largest known species is Garypus titanius of Ascension Island[3] at up to 12 mm (0.5 in).[4][5] Range is generally smaller at an average of 3 mm (0.1 in).[1]

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A pseudoscorpion from the United States

The abdomen, known as the opisthosoma, is made up of twelve segments, each protected by plates (called tergites above and sternites below) made of chitin. The abdomen is short and rounded at the rear, rather than extending into a segmented tail and stinger like true scorpions (the fact that they look exactly like scorpions, aside from not having a stinger tail, is the source of the name "Pseudoscorpion"). 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.[5]

A pseudoscorpion has eight legs with five to seven segments; 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 "finger", with a separate movable finger controlled by an adductor muscle. A venom gland and duct are usually located in the mobile finger; the venom is used to capture and immobilize the pseudoscorpion's prey. During digestion, pseudoscorpions pour a mildly corrosive fluid over the prey, then ingest the liquefied remains.

Pseudoscorpions spin silk from a gland in their jaws to make disk-shaped cocoons for mating, molting, or waiting out cold weather. However, they do not have book lungs like true scorpions and the Tetrapulmonata. Instead they breathe exclusively through trachea, which open laterally through two pairs of spiracles on the posterior margins of the sternites of abdominal segments 3 and 4.[6]

Behavior

"
Phoretic pseudoscorpion on a fly, Germany

Some species have an elaborate mating dance, where the male pulls a female over a spermatophore previously laid upon a surface.[7] In other species, the male also pushes the sperm into the female genitals using the forelegs.[8] The female carries the fertilized eggs in a brood pouch attached to her abdomen, and the young ride on the mother for a short time after they hatch.[2] Between 20 and 40 young are hatched in a single brood; there may be more than one brood per year. The young go through three molts over the course of several years before reaching adulthood. Many species molt in a small, silken igloo that protects them from enemies during this vulnerable period.[9] After reaching adulthood, pseudoscorpions live two to three 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,[10] others may sometimes be found feeding on mites under the wing covers of certain beetles.

Distribution

"
A book scorpion (Chelifer cancroides) on top of an open book
"
A coloured etching of a pseudoscorpion

There are more than 3,300 species of pseudoscorpions recorded in more than 430 genera, with more being discovered on a regular basis. They range worldwide, even in temperate to cold regions like Northern Ontario and above 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 like the Canary Islands, where around 25 endemic species have been found.[11] There are also two endemic species on the Maltese Islands.[1] Species have been found under tree bark, in leaf and pine litter, in soil, in tree hollows, under stones, in caves, at the seashore in the intertidal zone, and within fractured rocks.[2]

Chelifer cancroides is the species most commonly found in homes, where they are 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 like booklice and house dust mites. They enter homes by "riding along" attached to insects (known as phoresy). The insects employed are necessarily larger than the pseudoscorpion, or they are brought in with firewood.

Evolution

The oldest known fossil pseudoscorpion dates back 380 million years to the Devonian period.[12] It has all of the traits of a modern pseudoscorpion, indicating that the order evolved very early in the history of land animals.[13] 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.

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."[14]

Classification

The following taxon numbers are calculated as of the end of 2012.[15]

  • Order Pseudoscorpiones de Geer, 1778 (2 suborders)
  • † Family Dracochelidae Schawaller, Shear and Bonamo, 1991 (1 fossil genus, 1 fossil species)
  • Family Chthoniidae Daday, 1888 (28 genera, 650 species [3 fossil species])
  • Family Lechytiidae Chamberlin, 1929 (1 genus, 23 species [1 fossil species])
  • Family Pseudotyrannochthoniidae Beier, 1932 (5 genera, 49 species)
  • Family Tridenchthoniidae Balzan, 1892 (15 genera, 71 species [1 fossil genus, 1 fossil species])
  • Family Feaellidae Ellingsen, 1906 (1 genus, 12 species)
  • Family Pseudogarypidae Chamberlin, 1923 (2 genera, 7 species [5 fossil species])
  • Suborder Iocheirata Harvey, 1992 (5 superfamilies)
  • Family Bochicidae Chamberlin, 1930 (12 genera, 42 species)
  • Family Gymnobisiidae Beier, 1947 (4 genera, 11 species)
  • Family Hyidae Chamberlin, 1930 (2 genera, 14 species)
  • Family Ideoroncidae Chamberlin, 1930 (11 genera, 59 species)
  • Family Neobisiidae Chamberlin, 1930 (33 genera, 595 species [4 fossil species])
  • Family Parahyidae Harvey, 1992 (1 genus, 1 species)
  • Family Syarinidae Chamberlin, 1930 (18 genera, 111 species)
  • Family Garypidae Simon, 1879 (10 genera, 80 species)
  • Family Garypinidae Daday, 1888 (21 genera, 76 species [2 fossil species])
  • Family Geogarypidae Chamberlin, 1930 (3 genera, 60 species [3 fossil species])
  • Family Larcidae Harvey, 1992 (2 genera, 15 species)
  • Family Menthidae Chamberlin, 1930 (5 genera, 12 species)
  • Family Olpiidae Banks, 1895 (36 genera, 268 species)
  • Family Cheiridiidae Hansen, 1894 (7 genera, 73 species [1 fossil genus, 3 fossil species])
  • Family Pseudochiridiidae Chamberlin, 1923 (2 genera, 12 species [1 fossil species])
  • Family Atemnidae Kishida, 1929 (21 genera, 178 species [1 fossil genus, 1 fossil species])
  • Family Cheliferidae Risso, 1827 (58 genera, 273 species [5 fossil genus, 12 fossil species])
  • Family Chernetidae Menge, 1855 (117 genera, 663 species [1 fossil genus, 3 fossil species])
  • Family Withiidae Chamberlin, 1931 (36 genera, 158 species [1 fossil genus, 1 fossil species])

References

  1. ^ a b c Schembri, Patrick J.; Baldacchino, Alfred E. (2011). Ilma, Blat u Hajja: Is-Sisien tal-Ambjent Naturali Malti (in Maltese). p. 66. ISBN 978-99909-44-48-8.
  2. ^ a b c Pennsylvania State University, Department: Entomological Notes: Pseudoscorpion Fact Sheet
  3. ^ 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.
  4. ^ "Endemic invertebrates" (PDF). Ascension Island Conservation Centre. Archived from the original (PDF) on 2010-05-09.
  5. ^ a b "Pseudoscorpions". Agricultural Research Council (South Africa). Archived from the original on 2012-02-22.
  6. ^ Discontinuous gas exchange in a tracheate arthropod, the pseudoscorpion Garypus californicus: occurrence, characteristics and temperature dependence
  7. ^ 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.
  8. ^ Heather C. Proctor (1993). "Mating biology resolves trichotomy for cheliferoid pseudoscorpions (Pseudoscorpionida, Cheliferoidea)" (PDF). Journal of Arachnology. 21 (2): 156–158.
  9. ^ Ross Piper (2007). Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals. Greenwood Press.
  10. ^ "Pseudoscorpions". South African National Survey of Arachnids. Archived from the original on 2012-01-07.
  11. ^ 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.
  12. ^ 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.
  13. ^ Wolfgang Schawaller, William A. Shear & Patricia M. Bonamo (1991). "The first Paleozoic pseudoscorpions (Arachnida, Pseudoscorpionida)". American Museum Novitates. 3009. hdl:2246/5041.
  14. ^ Adams, George (1787): Essays on the Microscope. First edition. (London: Robert Hindmarsh)
  15. ^ Harvey, Mark S. (2013). Zhang, Z.-Q. (ed.). "Order Pseudoscorpiones In: Animal Biodiversity: An Outline of Higher-level Classification and Survey of Taxonomic Richness (Addenda 2013)". Zootaxa. 3703.
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Pseudoscorpion: Brief Summary

provided by wikipedia EN

A pseudoscorpion, also known as a false scorpion or book scorpion, is an arachnid belonging to the order Pseudoscorpiones, also known as Pseudoscorpionida or Chelonethida.

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

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