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{{Short description|Order of arachnids known as microwhip scorpions}}
{{Taxobox
{{Automatic taxobox
| name = Palpigradi
| name = Palpigradi
| image = Live Eukoenenia spelaea in its cave habitat.png
| image_caption = ''[[Eukoenenia spelaea]]''
| image = Live Eukoenenia spelaea in its cave habitat.png
| image_caption = ''[[Eukoenenia spelaea]]''
| fossil_range = {{Fossil range|Cenomanian|Recent}}
| fossil_range = {{Fossil range|Cenomanian|Recent}}
| regnum = [[Animal]]ia
| taxon = Palpigradi
| phylum = [[Arthropod]]a
| authority = [[Tamerlan Thorell|Thorell]], 1888<ref>{{Cite journal |last=Thorell |first=Tamerlan |date=1888 |title=Pedipalpi e Scorpioni dell'Arcipelago Malese conservati nel Museo Civico di Storia Naturale di Genova |journal=Annali del Museo Civico di Storia Naturale di Genova |volume=26 |pages=327–428}}</ref>
| classis = [[Arachnid]]a
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| subdivision_ranks = Families
| ordo = '''Palpigradi'''
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| subdivision =
| ordo_authority = [[Tamerlan Thorell|Thorell]], 1900
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* [[Eukoeneniidae]]
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| subdivision_ranks = Families & genera
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* [[Prokoeneniidae]]
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| subdivision =
| synonyms =
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;[[Eukoeneniidae]]
* Microthelyphonida<ref>Van der Hammen, L. (1982). Comparative studies in Chelicerata II. Epimerata (Palpigradi and Actinotrichida). ''Zoologische Verhandelingen'', ''196''(1), 1-70.</ref>
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*''[[Allokoenenia]]'' (1 species)
* Palpigradida{{Citation needed|date=June 2021}}
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*''[[Eukoenenia]]'' (60 species)
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*''[[Koeneniodes]]'' (8 species)
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*''[[Leptokoenenia]]'' (2 species)
*†''[[Electrokoenenia]]'' (1 species)<ref name=Electrokoenenia />
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;[[Prokoeneniidae]]
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*''[[Prokoenenia]]'' (6 species)
⚫
*''[[Triadokoenenia]]'' (1 species)
;''[[incertae sedis]]''
⚫
*†''[[Paleokoenenia]]'' (1 species)
}}
}}
'''Palpigrades''', commonly known as '''microwhip scorpions''', are arachnids belonging to the order '''Palpigradi.'''


'''Palpigradi''' is an order of very small arachnids commonly known as '''microwhip scorpion''' or '''palpigrades.'''
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==Description==
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Palpigrades belong to the [[arachnid]] class.<ref name="schembri"/> They are the sister group to [[Thelyphonida]], or whip scorpions,<ref name="Ax"/> no more than {{convert|3|mm|in}} in length,<ref name="schembri"/> and averaging {{convert|1|-|1.5|mm|2|abbr=on}}.<ref name="Ax">{{cite book |author=Peter Ax |year=2000 |title=Multicellular animals. The phylogenetic system of the Metazoa. Volume II |publisher=[[Springer Science+Business Media|Springer]] |isbn=978-3-540-67406-1 |chapter=Palpigradi – Holotracheata |pages=120–121}}</ref> They have a thin, pale, segmented [[integument]], and a segmented abdomen that terminates in a whip-like flagellum. This is made up of 15 segment-like parts, or "articles", and may make up as much as half the animal's length.<ref name="Nardi"/> Each article of the flagellum bears [[bristle]]s, giving the whole flagellum the appearance of a bottle brush.<ref name="Nardi"/> The carapace is divided into two plates between the third and fourth leg pair of legs. They have no eyes.


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== Description ==
As in some other arachnids, the first pair of legs is modified to serve as sensory organs, and are held clear of the ground while walking. Unusually, however, palpigrades use their [[pedipalp]]s for locomotion, so that the animal appears to be walking on five pairs of legs.<ref name="Nardi">{{cite book |author=James B. Nardi |year=2007 |title=Life in the soil: a guide for naturalists and gardeners |series=Chicago Lectures in Mathematics Series |publisher=[[University of Chicago Press]] |isbn=978-0-226-56852-2}}</ref>
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Palpigrades belong to the [[arachnid]] class.<ref name="schembri"/> They are the sister group to [[Solifugae]],<ref>{{Cite journal |last1=Ballesteros |first1=Jesús A. |last2=López |first2=Carlos E. Santibáñez |last3=Kováč |first3=Ľubomír |last4=Gavish-Regev |first4=Efrat |last5=Sharma |first5=Prashant P. |date=2019 |title=Ordered phylogenomic subsampling enables diagnosis of systematic errors in the placement of the enigmatic arachnid order Palpigradi |journal=[[Proceedings of the Royal Society#Proceedings of the Royal Society B: Biological Sciences|Proceedings of the Royal Society B]] |volume=286 |issue=1917 |pages=e20192426 |doi=10.1098/rspb.2019.2426|pmid=31847768 |pmc=6939912 |doi-access=free }}</ref> no more than {{convert|3|mm|in}} in length,<ref name="schembri"/> and averaging {{convert|1|-|1.5|mm|2|abbr=on}}.<ref name="Ax">{{cite book |author=Peter Ax |year=2000 |title=Multicellular animals. The phylogenetic system of the Metazoa. Volume II |publisher=[[Springer Science+Business Media|Springer]] |isbn=978-3-540-67406-1 |chapter=Palpigradi – Holotracheata |pages=120–121}}</ref> They have a thin, pale, segmented [[integument]], and a segmented abdomen that terminates in a whip-like flagellum. This is made up of 15 segment-like parts, or "articles", and may make up as much as half the animal's length.<ref name="Nardi"/> Each article of the flagellum bears [[bristle]]s, giving the whole flagellum the appearance of a bottle brush.<ref name="Nardi"/> The carapace is divided into two plates between the third and fourth leg pair of legs. They have no eyes.


As in some other arachnids, the first pair of legs is modified to serve as sensory organs, and are held clear of the ground while walking. Often, however, palpigrades use their [[pedipalp]]s for locomotion, so that the animal appears to be walking on five pairs of legs.<ref name="Nardi">{{cite book |author=James B. Nardi |year=2007 |title=Life in the soil: a guide for naturalists and gardeners |url=https://archive.org/details/lifesoilguidefor00nard |url-access=registration |series=Chicago Lectures in Mathematics Series |publisher=[[University of Chicago Press]] |isbn=978-0-226-56852-2}}</ref> But they do not swing in phase with the walking legs, and are mostly used as legs in rough terrain.<ref>[https://arachnology.org/arachnology/orders/palpigradi/behaviour.html Palpigradi: Behaviour - International Society of Arachnology]</ref> Both the nine-segmented pedipalps and the four pairs of legs end in three claws each. The first pair of legs are 11-segmented, the second and third pairs seven-segmented and the fourth pair eight-segmented.<ref>[https://edoc.ub.uni-muenchen.de/23809/1/Franz-Guess_Sandra.pdf Microscopic anatomy of Eukoenenia spelaea (Palpigradi)]</ref><ref>[https://www.european-arachnology.org/esa/wp-content/uploads/2015/08/345-354_Dunlop.pdf Character states and evolution of the chelicerate claws]</ref>
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Some palpigrades have three pairs of abdominal lung-sacs, although these are not true [[book lung]]s as there is no trace of the characteristic leaflike lamellae which defines book lungs. However, many species have no respiratory organs at all and breathe directly through the cuticle.<ref name=IZ>{{cite book |author= Barnes, Robert D. |year=1982 |title=Invertebrate Zoology |publisher= [[Saunders College]] |location= Philadelphia, PA |page=614 |isbn=0-03-056747-5}}</ref>


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The family Prokoeneniidae have three pairs of lung-sacs on the fourth, fifth and sixth abdominal segments, although these are not true [[book lung]]s as there is no trace of the characteristic leaflike lamellae which defines book lungs. Family Eukoeneniidae have no respiratory organs at all and breathe directly through the cuticle.<ref name=IZ>{{cite book |author= Barnes, Robert D. |year=1982 |title=Invertebrate Zoology |publisher= [[Saunders College]] |location= Philadelphia, PA |page=614 |isbn=0-03-056747-5}}</ref>
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Their exoskeleton is very weakly sclerotized compared to other arachnids, which is the reason why fossils are so rare, and go no further back than five million years ago.<ref>[https://books.google.no/books?id=68urAgAAQBAJ&pg=PA65&lpg=PA65&dq=palpigrades+appear+in+the+fossil+record,+but+only+about+five+million+years+ago&source=bl&ots=KarW9C503g&sig=ACfU3U1823HDEXJ_y8627qnFandAgMYtRQ&hl=no&sa=X&ved=2ahUKEwjXpdvOoLrlAhVJLpoKHcVWAxUQ6AEwAHoECAYQAQ#v=onepage&q=palpigrades%20appear%20in%20the%20fossil%20record%2C%20but%20only%20about%20five%20million%20years%20ago&f=false When the Invasion of Land Failed: The Legacy of the Devonian Extinctions]</ref>


⚫
Their [[Exoskeleton]] is very weakly sclerotized compared to other arachnids, which is the reason why fossils are so rare, and go no further back than 99 million years ago in Burmese Amber.<ref>[https://books.google.com/books?id=68urAgAAQBAJ&dq=palpigrades+appear+in+the+fossil+record%2C+but+only+about+five+million+years+ago&pg=PA65 When the Invasion of Land Failed: The Legacy of the Devonian Extinctions]</ref>
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==Ecology and behavior==

⚫
Species of Palpigradi live interstitially in wet [[Tropics|tropical]] and [[Subtropics|subtropical]] soils.<ref name="Ax"/> A few species have been found in shallow coral sands and on tropical beaches.<ref name="Geire">{{cite book |author=Olav Geire |year=2009 |title=Meiobenthology: the microscopic motile fauna of aquatic sediments |publisher=[[Springer Science+Business Media|Springer]] |isbn=978-3-540-68657-6 |chapter=Palpigradi (Arachnidae) |pages=205–206}}</ref> In Europe, they have been found in caves and underground spaces.<ref name=Smrz13/> There is one [[endemic species]] on the [[Malta (island)|island of Malta]], in the [[Mediterranean Sea]], which exists only in one specific cave.<ref name="schembri">{{cite book|last1=Schembri|first1=Patrick J.|last2=Baldacchino|first2=Alfred E.|title=Ilma, Blat u Hajja: Is-Sisien tal-Ambjent Naturali Malti|language=Maltese|url=http://www.bdlbooks.com/geography/3394-ilma-blat-u-hajja.html|isbn=978-99909-44-48-8|date=2011|page=66}}</ref> They need a damp environment to survive, and they always hide from light, so they are commonly found in the moist earth under buried stones and rocks. They can be found on every continent, except in Arctic and Antarctic regions. Terrestrial Palpigradi have [[Hydrophobe|hydrophobic]] [[cuticle]]s, but littoral (beach-dwelling) species are able to pass through the water surface easily.<ref name="Geire"/>
⚫
== Ecology and behavior ==
⚫
Species of Palpigradi live interstitially in wet [[Tropics|tropical]] and [[Subtropics|subtropical]] soils.<ref name="Ax"/> A few species have been found in shallow coral sands and on tropical beaches.<ref name="Geire">{{cite book |author=Olav Geire |year=2009 |title=Meiobenthology: the microscopic motile fauna of aquatic sediments |publisher=[[Springer Science+Business Media|Springer]] |isbn=978-3-540-68657-6 |chapter=Palpigradi (Arachnidae) |pages=205–206}}</ref> In Europe, they have been found in caves and underground spaces.<ref name=Smrz13/> There is one [[endemic species]] on the [[Malta (island)|island of Malta]], in the [[Mediterranean Sea]], which exists only in one specific cave.<ref name="schembri">{{cite book|last1=Schembri|first1=Patrick J.|last2=Baldacchino|first2=Alfred E.|title=Ilma, Blat u Hajja: Is-Sisien tal-Ambjent Naturali Malti|language=mt|url=http://www.bdlbooks.com/geography/3394-ilma-blat-u-hajja.html|isbn=978-99909-44-48-8|date=2011|page=66|publisher=Malta University Press }}</ref> They need a damp environment to survive, and they always hide from light, so they are commonly found in the moist earth under buried stones and rocks. They can be found on every continent, except in Arctic and Antarctic regions. Terrestrial Palpigradi have [[Hydrophobe|hydrophobic]] [[cuticle]]s, but littoral (beach-dwelling) species are able to pass through the water surface easily.<ref name="Geire"/>


Very little is known about palpigrade behavior.<ref name="Nardi"/> They are generally believed to be predators like their larger relatives, feeding on minuscule animals in their habitat.<ref name="Nardi"/> However, their chelicerae have been described as "more like a comb or brush than the forceps of a predator", and the species ''[[Eukoenenia spelaea]]'' has been shown to feed on [[cyanobacteria]] ("blue-green algae").<ref name=Smrz13/> Their mating habits are unknown, except that they lay only a few relatively large eggs at a time.<ref name="Nardi"/>
Very little is known about palpigrade behavior.<ref name="Nardi"/> They are generally believed to be predators like their larger relatives, feeding on minuscule animals in their habitat.<ref name="Nardi"/> However, their chelicerae have been described as "more like a comb or brush than the forceps of a predator", and the species ''[[Eukoenenia spelaea]]'' has been shown to feed on [[cyanobacteria]] ("blue-green algae").<ref name=Smrz13/> Their mating habits are unknown, except that they lay only a few relatively large eggs at a time.<ref name="Nardi"/>


==Classification==
== Classification ==
By 2003, approximately 79 species of palpigrades had been described worldwide, in two families, containing a total of 7 genera.<ref>{{cite book |author=Mark S. Harvey |year=2003 |title=Catalogue of the smaller arachnid orders of the world: Amblypygi, Uropygi, Schizomida, Palpigradi, Ricinulei and Solifugae |publisher=[[CSIRO Publishing]] |isbn=978-0-643-06805-6 |chapter=Order Palpigradi Thorell |pages=151–174}}</ref> The two families are differentiated by the presence of ventral sacs on [[sternite]]s IV–VI in [[Prokoeneniidae]], and their absence in [[Eukoeneniidae]].<ref>{{cite book |author1=Joel Cracraft |author2=Michael J. Donoghue |lastauthoramp=yes |year=2004 |title=Assembling the tree of life |publisher=[[Oxford University Press]] |isbn=978-0-19-517234-8 |chapter=Palpigrades (Palpigradi) |pages=302}}</ref>
Palpigradi is split into two families, differentiated by the presence of ventral sacs on [[sternite]]s IV–VI in [[Prokoeneniidae]], and their absence in [[Eukoeneniidae]].<ref>{{cite book |author1=Joel Cracraft |author-link1=Joel Cracraft |author2=Michael J. Donoghue |name-list-style=amp |year=2004 |title=Assembling the tree of life |url=https://archive.org/details/assemblingtreeli00crac_056 |url-access=registration |publisher=[[Oxford University Press]] |isbn=978-0-19-517234-8 |chapter=Palpigrades (Palpigradi) |pages=[https://archive.org/details/assemblingtreeli00crac_056/page/n318 302]}}</ref>


Two fossil palpigrade species have been described. The first one is from the [[Onyx Marble]] of [[Arizona]], which is probably of [[Pliocene]] age.<ref>{{cite journal |author1=J. Mark Rowland |author2=W. David Sissom |lastauthoramp=yes |year=1980 |title=Report on a fossil palpigrade from the Tertiary of Arizona, and a review of the morphology and systematics of the order (Arachnida: Palpigradida) |journal=[[Journal of Arachnology]] |volume=8 |pages=69–86 |jstor=3705206}}</ref> Its familial position is uncertain. The second one (''[[Electrokoenenia]] yaksha''), belonging to the family Eukoeneniidae, is known from [[Cretaceous]] ([[Cenomanian]]) amber from northern [[Myanmar]].<ref name=Electrokoenenia>{{Cite journal|author1=Michael S. Engel |author2=Laura C. V. Breitkreuz |author3=Chenyang Cai |author4=Mabel Alvarado |author5=Dany Azar |author6=Diying Huang |year=2016 |title=The first Mesozoic microwhip scorpion (Palpigradi): a new genus and species in mid-Cretaceous amber from Myanmar |journal=The Science of Nature |volume=103 |issue=3–4 |pages=19 |doi=10.1007/s00114-016-1345-4 }}</ref> Older publications refer to a fossil palpigrade (or palpigrade-like animal) from the [[Jurassic]] of the [[Solnhofen limestone]] in Germany,<ref>{{cite journal | last1 = Haase | first1 = E | year = 1890 | title = Beitrag zur Kenntniss der fossilen Arachniden | url = | journal = Zeitschrift der Deutsche geologische Gesellschaft | volume = 1890 | issue = | pages = 629–657 }}</ref> but this has now been shown to be a misidentified fossil insect.<ref>{{cite journal |author1=Xavier Delclòs |author2=André Nel |author3=Dany Azar |author4=Günter Bechly |author5=Jason A. Dunlop |author6=Michael S. Engel |author7=Sam W. Heads |year=2008 |title=The enigmatic Mesozoic insect taxon Chresmodidae (Polyneoptera): New palaeobiological and phylogenetic data, with the description of a new species from the Lower Cretaceous of Brazil |journal=[[Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen]] |volume=247 |pages=353–381 |url=http://www.schweizerbart.de/resources/downloads/paper_previews/59265.pdf |format=[[Portable Document Format|PDF]] |doi=10.1127/0077-7749/2008/0247-0353}}</ref>
Two fossil palpigrade species have been described. The first one is from the [[Onyx Marble]] of [[Arizona]], which is probably of [[Pliocene]] age.<ref>{{cite journal |author1=J. Mark Rowland |author2=W. David Sissom |name-list-style=amp |year=1980 |title=Report on a fossil palpigrade from the Tertiary of Arizona, and a review of the morphology and systematics of the order (Arachnida: Palpigradida) |journal=[[Journal of Arachnology]] |volume=8 |issue=1 |pages=69–86 |jstor=3705206}}</ref> Its familial position is uncertain. The second one (''[[Electrokoenenia yaksha]]''), belonging to the family Eukoeneniidae, is known from [[Cretaceous]] ([[Cenomanian]]) [[Burmese amber]] from northern [[Myanmar]].<ref name=Electrokoenenia>{{Cite journal|author1=Michael S. Engel |author2=Laura C. V. Breitkreuz |author3=Chenyang Cai |author4=Mabel Alvarado |author5=Dany Azar |author6=Diying Huang |year=2016 |title=The first Mesozoic microwhip scorpion (Palpigradi): a new genus and species in mid-Cretaceous amber from Myanmar |journal=The Science of Nature |volume=103 |issue=3–4 |pages=19 |doi=10.1007/s00114-016-1345-4 |pmid=26879963 |bibcode=2016SciNa.103...19E |s2cid=14816297 }}</ref> Older publications refer to a fossil palpigrade (or palpigrade-like animal) from the [[Jurassic]] of the [[Solnhofen limestone]] in Germany,<ref>{{cite journal | last1 = Haase | first1 = E | year = 1890 | title = Beitrag zur Kenntniss der fossilen Arachniden | journal = Zeitschrift der Deutsche geologische Gesellschaft | volume = 1890 | pages = 629–657 }}</ref> but this has now been shown to be a misidentified fossil insect.<ref>{{cite journal |author1=Xavier Delclòs |author2=André Nel |author3=Dany Azar |author4=Günter Bechly |author5=Jason A. Dunlop |author6=Michael S. Engel |author7=Sam W. Heads |year=2008 |title=The enigmatic Mesozoic insect taxon Chresmodidae (Polyneoptera): New palaeobiological and phylogenetic data, with the description of a new species from the Lower Cretaceous of Brazil |journal=[[Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen]] |volume=247 |issue=3 |pages=353–381 |url=http://www.schweizerbart.de/resources/downloads/paper_previews/59265.pdf |doi=10.1127/0077-7749/2008/0247-0353}}</ref>

=== Genera ===
{{as of|2022|09}}, the World Palpigradi Catalog accepts the following eight genera:<ref name="NMBE">{{cite web |date=2022 |title=World Palpigradi Catalog |url=https://wac.nmbe.ch/order/palpigradi/2 |access-date=25 September 2022 |website=World Palpigradi Catalog |publisher=Natural History Museum Bern}}</ref>
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* ''[[Allokoenenia]]'' <small>Silvestri, 1913</small>
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* ''[[Eukoenenia]]'' <small>Börner, 1901</small>
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* ''[[Koeneniodes]]'' <small>Silvestri, 1913</small>
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* ''[[Leptokoenenia]]'' <small>Condé, 1965</small>
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* ''[[Prokoenenia]]'' <small>Börner, 1901</small>
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* ''[[Triadokoenenia]]'' <small>Condé, 1991</small>
* †''[[Electrokoenenia]]'' <small>Engel & Huang, 2016</small>
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* †''[[Paleokoenenia]]'' <small>Rowland & Sissom, 1980</small>
{{Clear}}
{{Clear}}


==See also==
== See also ==
{{Portal|Arthropods}}
{{Portal|Arthropods}}

* [[Maltese palpigrade]]
* [[Maltese palpigrade]]


==References==
== References ==
{{Reflist|2|refs=
{{Reflist|2|refs=


<ref name=Smrz13>{{Cite journal |last1=Smrž |first1=Jaroslav |first2=Ĺubomír |last2=Kováč |first3=Jaromír |last3=Mikeš |first4=Alena |last4=Lukešová |date=2013 |title=Microwhip Scorpions (Palpigradi) Feed on Heterotrophic Cyanobacteria in Slovak Caves – A Curiosity among Arachnida |journal=PLoS ONE |volume=8 |issue=10 |page=e75989 |doi=10.1371/journal.pone.0075989 |lastauthoramp=yes |pmid=24146804 |pmc=3797709}}</ref>
<ref name=Smrz13>{{Cite journal |last1=Smrž |first1=Jaroslav |first2=Ľubomír |last2=Kováč |first3=Jaromír |last3=Mikeš |first4=Alena |last4=Lukešová |date=2013 |title=Microwhip Scorpions (Palpigradi) Feed on Heterotrophic Cyanobacteria in Slovak Caves – A Curiosity among Arachnida |journal=PLOS ONE |volume=8 |issue=10 |page=e75989 |doi=10.1371/journal.pone.0075989 |name-list-style=amp |pmid=24146804 |pmc=3797709|bibcode=2013PLoSO...875989S |doi-access=free }}</ref>


}}
}}

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{{Wikispecies}}
== External links ==
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* {{Wikispecies-inline}}


{{Arachnida}}
{{Arachnida}}
{{Taxonbar|from=Q19117}}
{{Taxonbar|from=Q19117}}
{{Authority control}}


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[[Category:Palpigradi| ]]
[[Category:Cave arachnids]]
[[Category:Cave arachnids]]
[[Category:Arachnid orders]]
[[Category:Arachnid orders]]
[[Category:Cenomanian first appearances]]
[[Category:Cenomanian first appearances]]
[[Category:Extant Late Cretaceous first appearances]]
[[Category:Extant Cenomanian first appearances]]
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[[Category:Palpigradi| ]]

Revision as of 11:39, 25 June 2024

Palpigradi
Temporal range: Cenomanian–Recent
Eukoenenia spelaea
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Chelicerata
Class: Arachnida
Order: Palpigradi
Thorell, 1888[1]
Families
Synonyms

Palpigradi is an order of very small arachnids commonly known as microwhip scorpion or palpigrades.

Description

Palpigrades belong to the arachnid class.[3] They are the sister group to Solifugae,[4] no more than 3 millimetres (0.12 in) in length,[3] and averaging 1–1.5 mm (0.04–0.06 in).[5] They have a thin, pale, segmented integument, and a segmented abdomen that terminates in a whip-like flagellum. This is made up of 15 segment-like parts, or "articles", and may make up as much as half the animal's length.[6] Each article of the flagellum bears bristles, giving the whole flagellum the appearance of a bottle brush.[6] The carapace is divided into two plates between the third and fourth leg pair of legs. They have no eyes.

As in some other arachnids, the first pair of legs is modified to serve as sensory organs, and are held clear of the ground while walking. Often, however, palpigrades use their pedipalps for locomotion, so that the animal appears to be walking on five pairs of legs.[6] But they do not swing in phase with the walking legs, and are mostly used as legs in rough terrain.[7] Both the nine-segmented pedipalps and the four pairs of legs end in three claws each. The first pair of legs are 11-segmented, the second and third pairs seven-segmented and the fourth pair eight-segmented.[8][9]

The family Prokoeneniidae have three pairs of lung-sacs on the fourth, fifth and sixth abdominal segments, although these are not true book lungs as there is no trace of the characteristic leaflike lamellae which defines book lungs. Family Eukoeneniidae have no respiratory organs at all and breathe directly through the cuticle.[10]

Their Exoskeleton is very weakly sclerotized compared to other arachnids, which is the reason why fossils are so rare, and go no further back than 99 million years ago in Burmese Amber.[11]

Ecology and behavior

Species of Palpigradi live interstitially in wet tropical and subtropical soils.[5] A few species have been found in shallow coral sands and on tropical beaches.[12] In Europe, they have been found in caves and underground spaces.[13] There is one endemic species on the island of Malta, in the Mediterranean Sea, which exists only in one specific cave.[3] They need a damp environment to survive, and they always hide from light, so they are commonly found in the moist earth under buried stones and rocks. They can be found on every continent, except in Arctic and Antarctic regions. Terrestrial Palpigradi have hydrophobic cuticles, but littoral (beach-dwelling) species are able to pass through the water surface easily.[12]

Very little is known about palpigrade behavior.[6] They are generally believed to be predators like their larger relatives, feeding on minuscule animals in their habitat.[6] However, their chelicerae have been described as "more like a comb or brush than the forceps of a predator", and the species Eukoenenia spelaea has been shown to feed on cyanobacteria ("blue-green algae").[13] Their mating habits are unknown, except that they lay only a few relatively large eggs at a time.[6]

Classification

Palpigradi is split into two families, differentiated by the presence of ventral sacs on sternites IV–VI in Prokoeneniidae, and their absence in Eukoeneniidae.[14]

Two fossil palpigrade species have been described. The first one is from the Onyx Marble of Arizona, which is probably of Pliocene age.[15] Its familial position is uncertain. The second one (Electrokoenenia yaksha), belonging to the family Eukoeneniidae, is known from Cretaceous (Cenomanian) Burmese amber from northern Myanmar.[16] Older publications refer to a fossil palpigrade (or palpigrade-like animal) from the Jurassic of the Solnhofen limestone in Germany,[17] but this has now been shown to be a misidentified fossil insect.[18]

Genera

As of September 2022, the World Palpigradi Catalog accepts the following eight genera:[19]

See also

References

  1. ^ Thorell, Tamerlan (1888). "Pedipalpi e Scorpioni dell'Arcipelago Malese conservati nel Museo Civico di Storia Naturale di Genova". Annali del Museo Civico di Storia Naturale di Genova. 26: 327–428.
  2. ^ Van der Hammen, L. (1982). Comparative studies in Chelicerata II. Epimerata (Palpigradi and Actinotrichida). Zoologische Verhandelingen, 196(1), 1-70.
  3. ^ a b c 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.
  4. ^ Ballesteros, Jesús A.; López, Carlos E. Santibáñez; Kováč, Ľubomír; Gavish-Regev, Efrat; Sharma, Prashant P. (2019). "Ordered phylogenomic subsampling enables diagnosis of systematic errors in the placement of the enigmatic arachnid order Palpigradi". Proceedings of the Royal Society B. 286 (1917): e20192426. doi:10.1098/rspb.2019.2426. PMC 6939912. PMID 31847768.
  5. ^ a b Peter Ax (2000). "Palpigradi – Holotracheata". Multicellular animals. The phylogenetic system of the Metazoa. Volume II. Springer. pp. 120–121. ISBN 978-3-540-67406-1.
  6. ^ a b c d e f James B. Nardi (2007). Life in the soil: a guide for naturalists and gardeners. Chicago Lectures in Mathematics Series. University of Chicago Press. ISBN 978-0-226-56852-2.
  7. ^ Palpigradi: Behaviour - International Society of Arachnology
  8. ^ Microscopic anatomy of Eukoenenia spelaea (Palpigradi)
  9. ^ Character states and evolution of the chelicerate claws
  10. ^ Barnes, Robert D. (1982). Invertebrate Zoology. Philadelphia, PA: Saunders College. p. 614. ISBN 0-03-056747-5.
  11. ^ When the Invasion of Land Failed: The Legacy of the Devonian Extinctions
  12. ^ a b Olav Geire (2009). "Palpigradi (Arachnidae)". Meiobenthology: the microscopic motile fauna of aquatic sediments. Springer. pp. 205–206. ISBN 978-3-540-68657-6.
  13. ^ a b Smrž, Jaroslav; Kováč, Ľubomír; Mikeš, Jaromír & Lukešová, Alena (2013). "Microwhip Scorpions (Palpigradi) Feed on Heterotrophic Cyanobacteria in Slovak Caves – A Curiosity among Arachnida". PLOS ONE. 8 (10): e75989. Bibcode:2013PLoSO...875989S. doi:10.1371/journal.pone.0075989. PMC 3797709. PMID 24146804.
  14. ^ Joel Cracraft & Michael J. Donoghue (2004). "Palpigrades (Palpigradi)". Assembling the tree of life. Oxford University Press. pp. 302. ISBN 978-0-19-517234-8.
  15. ^ J. Mark Rowland & W. David Sissom (1980). "Report on a fossil palpigrade from the Tertiary of Arizona, and a review of the morphology and systematics of the order (Arachnida: Palpigradida)". Journal of Arachnology. 8 (1): 69–86. JSTOR 3705206.
  16. ^ Michael S. Engel; Laura C. V. Breitkreuz; Chenyang Cai; Mabel Alvarado; Dany Azar; Diying Huang (2016). "The first Mesozoic microwhip scorpion (Palpigradi): a new genus and species in mid-Cretaceous amber from Myanmar". The Science of Nature. 103 (3–4): 19. Bibcode:2016SciNa.103...19E. doi:10.1007/s00114-016-1345-4. PMID 26879963. S2CID 14816297.
  17. ^ Haase, E (1890). "Beitrag zur Kenntniss der fossilen Arachniden". Zeitschrift der Deutsche geologische Gesellschaft. 1890: 629–657.
  18. ^ Xavier Delclòs; André Nel; Dany Azar; Günter Bechly; Jason A. Dunlop; Michael S. Engel; Sam W. Heads (2008). "The enigmatic Mesozoic insect taxon Chresmodidae (Polyneoptera): New palaeobiological and phylogenetic data, with the description of a new species from the Lower Cretaceous of Brazil" (PDF). Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen. 247 (3): 353–381. doi:10.1127/0077-7749/2008/0247-0353.
  19. ^ "World Palpigradi Catalog". World Palpigradi Catalog. Natural History Museum Bern. 2022. Retrieved 25 September 2022.
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