Polyxenida

{{Short description|Order of millipedes}} {{Distinguish|Polyxenidas}} {{Redirect-distinguish-text|Bristle millipede|the bristly millipede, ''Polyxenus lagurus''}} {{Automatic taxobox | fossil_range = {{fossilrange|Barremian|Present}} | image = Polyxenus.lagurus.1.jpg | image_caption = ''Polyxenus lagurus'' | parent_authority = Latrielle, 1831 | taxon = Polyxenida | authority = Verhoeff, 1934 | subdivision_ranks = Families | subdivision_ref = <ref name=MilliBase2025/><ref name=ShortVahtera2017/> | subdivision = *Lophoproctidae *Polyxenidae *Synxenidae | synonyms = '''Subclass''' Pselaphognatha Latzel, 1884 Schizocephala Verhoeff, 1926 '''Order''' Ancyrotricha Cook, 1895 }} [[File:Polyxenida segmentation.jpg|thumb|Segmentation of Polyxenida millipedes. From top to bottom: ''Lophoturus madecassus'' Other Lophoproctidae and Polyxenidae ''Condexenus biramipalpus'' and ''Phryssonotus brevicapensis'' Other ''Phryssonotus'' ]]

'''Polyxenida''' is an order of millipedes readily distinguished by a unique body plan consisting of a soft, non-calcified body ornamented with tufts of bristles. These features have inspired the common names '''bristly millipedes''' or '''pincushion millipedes'''.<ref>{{Cite book |last1=Hennen |first1=Derek |url=https://ohiodnr.gov/static/documents/wildlife/backyard-wildlife/Millipedes+of+Ohio+Pub+5527.pdf |title=Millipedes of Ohio |last2=Brown |first2=Jeff |publisher=Ohio Division of Wildlife |pages=3, 16–17 |language=English}}</ref><ref>{{Cite web |title=Order Polyxenida - Bristly Millipedes |url=https://bugguide.net/node/view/19104 |access-date=2024-07-23 |website=bugguide.net}}</ref> This order includes about 148 species in four families worldwide, which represent the only living members of the subclass '''Penicillata'''.<ref name=":0" /><ref name="NguyenDuy2003">{{cite journal |last=Nguyen Duy-Jacquemin |first=M. |author2=J.-J. Geoffroy |year=2003 |title=A revised comprehensive checklist, relational database, and taxonomic system of reference for the bristly millipedes of the world (Diplopoda, Polyxenida) |url=https://journals.co.za/doi/abs/10.10520/EJC84512 |journal=African Invertebrates |volume=44 |issue=1 |pages=89–101}}</ref>

== Description ==

Polyxenida differ from other millipedes in having a soft, non-calcified exoskeleton, unique tufts of bristles or setae, fewer legs (no more than 17 pairs), and an absence of copulatory appendages in males.<ref name=":3">{{Cite book |last=Blower |first=J. Gordon |title=Millipedes : keys and notes for the identification of the species |date=1985 |publisher=Published for the Linnean Society of London and the Estuarine and Brackish-Water Sciences Association by E.J. Brill |others=Linnean Society of London, Estuarine and Brackish-water Sciences Association |isbn=90-04-07698-0 |location=London |oclc=13439686}}</ref><ref name=":0" /> Individuals are small, usually 1.5 to 4 millimeters (0.06 to 0.16 inches) long and not exceeding 7 millimeters (0.28 inches) long.<ref name=":0" /><ref name="NguyenDuy2003" /> Adults in most species have 13 pairs of legs, but in one species (''Lophoturus madecassus''), they have only 11 pairs of legs, and in one genus (''Phryssonotus''), they have 17 pairs of legs, except for one species (''Phryssonotus brevicapensis'') in which they (along with those in one other species, ''Condexenus biramipalpus'') have 15 pairs of legs.<ref name=":0">{{Cite journal|last1=Enghoff|first1=Henrik|last2=Golovatch|first2=Sergei|last3=Short|first3=Megan|last4=Stoev|first4=Pavel|last5=Wesener|first5=Thomas|date=2015-01-01|title=Diplopoda — taxonomic overview|url=https://brill.com/view/book/edcoll/9789004188273/B9789004188273_017.xml|journal=Treatise on Zoology - Anatomy, Taxonomy, Biology. The Myriapoda, Volume 2|language=en|pages=363–453|doi=10.1163/9789004188273_017|isbn=978-90-04-15612-8 |url-access=subscription}}</ref><ref name="NguyenDuy" />

== Defense ==

Bristly millipedes lack the chemical defenses and hard exoskeleton of other millipedes. Instead, these millipedes employ a unique defense mechanism: Bristles at the rear end of these millipedes feature hooks and barbs. These distinctive barbed bristles can easily detach and become entangled in the limbs and mouth-parts of predatory insects, effectively immobilizing them.<ref name="NADIPLOCHILO Penicllates">{{cite web |last=Shelley |first=Rowland M. |title=The Myriapoda (Millipedes, Centipedes) Featuring the North American Fauna |url=http://www.nadiplochilo.com/milli.html#P&C |url-status=usurped |archive-url=https://web.archive.org/web/20131030044827/http://nadiplochilo.com/milli.html |archive-date=30 October 2013 |access-date=30 October 2013}}</ref><ref>{{cite journal|last=Eisner|first=T|author2=Eisner, M |author3=Deyrup, M |title=Millipede defense: use of detachable bristles to entangle ants|journal=Proceedings of the National Academy of Sciences of the United States of America|year=1996|volume=93|issue=20|pages=10848–51|doi=10.1073/pnas.93.20.10848|pmid=8855269|pmc=38244|bibcode=1996PNAS...9310848E|doi-access=free}}</ref>

== Reproduction ==

Male Polyxenidans lack the modified sperm-transferring appendages (gonopods) found in most other millipede groups. Instead, sperm transfer is indirect: Males deposit spermatophores into webs that they construct. Females then find these spermatophores by following threads spun by the males and pick up the spermatophores with their genitalia.<ref name="Shelley 1999">{{cite journal|last=Shelley|first=Rowland M.|title=Centipedes and Millipedes with Emphasis on North American Fauna|journal=The Kansas School Naturalist|year=1999|volume=45|issue=3|pages=1–16|url=http://www.emporia.edu/ksn/v45n3-march1999/|access-date=2013-10-12|archive-url=https://web.archive.org/web/20161112025334/http://www.emporia.edu/ksn/v45n3-march1999/|archive-date=2016-11-12|url-status=dead}}</ref><ref name=":3" />

At least two species reproduce asexually by way of parthenogenesis, wherein females lay eggs without mating and males are absent or rare.<ref name=":0" /><ref name="IZ 1987">{{cite book|last=Barnes|first=Robert D.|title=Invertebrate zoology|year=1987|publisher=Saunders College Pub.|location=Philadelphia|pages=674–683|edition=5th|chapter=15. The myriapods}}</ref> For example, studies of the common species ''Polyxenus lagurus'' have found males scarce or absent in parts of northeastern Europe. Authorities suspect that in these populations, this species reproduces by thelytoky, that is, parthenogenesis in which unfertilized females produce female offspring.<ref>{{Cite journal |last=Enghoff |first=Henrik |date=1976 |title=Morphological comparison of bisexual and parthenogenetic Polyxenus lagurus (Linne, 1758) (Diplopoda Polyxenidae) in Denmark and Southern Sweden, with notes on taxonomy, distribution and ecology |url=https://danbif.dk/research-files/litteratur/entomologiske-meddelelser/bind-44/enghoff__h._1976c.pdf |journal=Entomologiske Meddelelser |volume=44 |pages=161–182}}</ref>

== Development == Millipedes in this order grow and develop through a series of molts, adding segments and legs until they reach a fixed number in the adult stage, which is the same in a given species. Adults continue to molt, but they do not add segments or legs. This mode of development is known as hemianamorphosis.<ref name=":12">{{Cite journal |last1=Enghoff |first1=Henrik |last2=Dohle |first2=Wolfgang |last3=Blower |first3=J. Gordon |date=1993 |title=Anamorphosis in Millipedes (Diplopoda) — The Present State of Knowledge with Some Developmental and Phylogenetic Considerations |url=https://academic.oup.com/zoolinnean/article-abstract/109/2/103/2646268?redirectedFrom=fulltext |journal=Zoological Journal of the Linnean Society |volume=109 |issue=2 |pages=103–234 |doi=10.1111/j.1096-3642.1993.tb00305.x|url-access=subscription }}</ref>

The typical pattern in this order is observed in the common species ''Polyxenus lagurus''. In this species, millipedes hatch with only 3 pairs of legs and 4 tergites, then develop through a series of seven molts and emerge as adults with 13 leg pairs and 10 tergites in the eighth stage. In this process, this millipede goes through stages with 3, 4, 5, 6, 8, 10, 12, and 13 leg pairs. Species in which adults have a different number of legs deviate from this common pattern.<ref name=":12" />

== Classification == [[File:Phryssonotus brevicapensis.jpg|thumb|''Phryssonotus brevicapensis'' (Synxenidae), a species from South Africa described in 2011<ref name=NguyenDuy/>]] Polyxenida is the only living order of the subclass Penicillata, the basal subclass of millipedes. Penicillata is the sister group of all other living millipedes, which form the subclass Chilognatha. The subclass Chilognatha contains the infraclasses Pentazonia and Helminthomorpha.<ref name=SierBond2007>{{cite journal|last=Sierwald|first=Petra|author2=Bond, Jason E.|title=Current Status of the Myriapod Class Diplopoda (Millipedes): Taxonomic Diversity and Phylogeny|journal=Annual Review of Entomology|year=2007|volume=52|issue=1|pages=401–420|doi=10.1146/annurev.ento.52.111805.090210|pmid=17163800}}</ref><ref name="Shear2011">{{cite journal|last=Shear|first=W|title=Class Diplopoda de Blainville in Gervais, 1844. ''In:'' Zhang, Z.-Q.(ed.) Animal biodiversity : an outline of higher-level classification and survey of taxonomic richness|journal=Zootaxa|year=2011|volume=3148|pages=159–164|url=http://www.mapress.com/zootaxa/2011/f/zt03148p164.pdf|doi=10.11646/zootaxa.3148.1.32}}</ref>

The order Polyxenida includes 165 species distributed among 33 genera.<ref>{{Cite web |title=Polyxenida Verhoeff, 1934 {{!}} COL |url=https://www.catalogueoflife.org/data/taxon/B6M7G |access-date=2025-07-24 |website=www.catalogueoflife.org}}</ref> At least eight new species have been described since 2010.<ref name=NguyenDuy>{{cite journal|last=Nguyen Duy - Jacquemin|first=Monique|author2=Uys, Charmaine |author3=Geoffroy, Jean-Jacques |title=Two remarkable new species of Penicillata (Diplopoda, Polyxenida) from Table Mountain National Park (Cape Town, South Africa)|journal=ZooKeys|issue=156|year=2011|pages=85–103|doi=10.3897/zookeys.156.2211|pmc=3253573|pmid=22303097|doi-access=free}}</ref><ref name=Short2011>{{cite journal|last=Short|first=Megan|author2=Huynh, Cuong|title=The genus Unixenus Jones, 1944 (Diplopoda, Penicillata, Polyxenida) in Australia|journal=ZooKeys|year=2011|issue=156|pages=105–122|doi=10.3897/zookeys.156.2168|pmid=22303098|url=https://www.pensoft.net/journals/zookeys/article/2168/the-genus-unixenus-jones-1944-diplopoda-penicillata-polyxenida-in-australia|pmc=3253574|doi-access=free}}</ref><ref name="short 2013">{{cite journal|last=Short|first=Megan|author2=Huynh, Cuong|title=Four new species of Unixenus Jones, 1944 (Diplopoda, Penicillata, Polyxenida) from Australia|journal=ZooKeys|year=2013|issue=278|pages=75–90|doi=10.3897/zookeys.278.4765|url=https://www.pensoft.net/journal_home_page.php?journal_id=1&page=article&SESID=e3cb6a83b169d0bb23a35cf247305d1e&type=show&article_id=4765&issue_id=382&ttar=da&search=Polyxenida&IN=Journals&TIP=&Image100_x=0&Image100_y=0&|pmid=23794829|pmc=3677348|doi-access=free}}</ref>

It contains the following subdivisions:<ref name=MilliBase2025/><ref name=ShortVahtera2017/>

* Superfamily Polyxenoidea Lucas, 1840 ** Family Lophoproctidae Silvestri, 1897 ** Family Polyxenidae Lucas, 1840 *** Subfamily Hypogexeninae Schubart, 1947 *** Subfamily Macroxeninae Condé, 2008 *** Subfamily Monographinae Condé, 2008 *** Subfamily Polyxeninae Lucas, 1840 * Superfamily Synxenoidea Silvestri, 1923 ** Family Synxenidae Silvestri, 1923

A phylogenetic analysis by Short & Vahtera in 2017 recovered the following phylogenetic trees, with both trees finding the family Polyxenidae polyphyletic, only the first recovering a division of the order into the two superfamilies, and only the second finding Lophoproctidae monophyletic:<ref name=ShortVahtera2017/>

{{col-begin|width=100%}} {{col-break}} '''Optimal maximum likelihood tree on molecular data'''<ref name=ShortVahtera2017/> {{clade| style=font-size:85%;line-height:85% |label1=Polyxenida |1={{clade |1=Synxenidae |2={{clade |1=Polyxeninae (Polyxenidae) |2={{clade |1=Macroxeninae (Polyxenidae) |2={{clade |grouplabel1={{clade labels |label1=Lophoproctidae |top1=75%}} |1=''Lophoproctus'' |barbegin1=red |2={{clade |1=''Alloproctoides'' + ''Lophoturus'' |barend1=red |2=Monographinae (Polyxenidae) }} }} }} }} }} }} {{col-break}} '''Strict consensus of most parsimonious trees on combined morphological and molecular data'''<ref name=ShortVahtera2017/> {{clade| style=font-size:85%;line-height:85% |label1=Polyxenida |1={{clade |grouplabel1={{clade labels |label1=Polyxeninae (Polyxenidae) |top1=75%}} |1= remaining ''Propolyxenus'' species |barbegin1=blue |2={{clade |1=''Polyxenus'' + ''Propolyxenus trivittatus'' |barend1=blue |2={{clade |1=Macroxeninae (Polyxenidae) |2={{clade |1=Lophoproctidae |2={{clade |grouplabel1={{clade labels |label1=Monographinae (Polyxenidae) |top1=75%}} |1=''Eudigraphis'' |barbegin1=green |2={{clade |1=''Monographis'' + ''Unixenus'' |barend1=green |2=Synxenidae }} }} }} }} }} }} }} {{col-end}}

From this analysis the authors concluded that the currently held taxonomic arrangement, of a family Polyxenidae with 4 subfamilies, may need to be further revised with elevation to family status of the subfamilies Monographinae and Polyxeninae. Additional material from a wider range of species is needed for a more definite picture of the internal interrelations of the group.<ref name=ShortVahtera2017/>

==Fossil history== The earliest representatives of Polyxenida are found in Lebanese amber from the Early Cretaceous period. The fossil records also include representatives found in Burmese amber, Baltic amber, and the Cretaceous amber of Haute-Provence in France. These fossils indicate that the families Polyxenidae and Synxenidae already existed in the Cretaceous period.<ref>{{cite journal |last=Duy-Jacquemin |first=MN |author2=Azar, D |year=2004 |title=The oldest records of Polyxenida (Myriapoda, Diplopoda): New discoveries from the Cretaceous ambers of Lebanon and France |url=https://sciencepress.mnhn.fr/en/periodiques/geodiversitas/26/4/les-plus-anciens-polyxenida-myriapoda-diplopoda-decouverts-recemment-dans-l-ambre-cretace-du-liban-et-de-france |journal=Geodiversitas |volume=26 |issue=4 |pages=631–641}}</ref>

Some authors place the extinct orders Arthropleurida and Eoarthropleurida (each represented by a single genus) within the Penicillata as a sister group to Polyxenida.<ref name="Kraus 2003">{{cite journal|last=Kraus|first=O|author2=C. Brauckman|title=Fossil giants and surviving dwarfs. Arthropleurida and Pselaphognatha (Ateolocerata, Diplopoda): characters, phylogenetic relationships and construction|journal=Verh. Naturwiss. Ver. Hamburg|year=2003|volume=40|issue=5|pages=5–50}}</ref> Others consider these extinct orders to be a sister group to Penicillata. Still others deem these extinct orders to be a sister group to the subclass Chilognatha instead.<ref name="Shear2010">{{cite journal |last=Shear |first=William A. |author2=Edgecombe, Gregory D. |year=2010 |title=The geological record and phylogeny of the Myriapoda |journal=Arthropod Structure & Development |volume=39 |issue=2–3 |pages=174–190 |doi=10.1016/j.asd.2009.11.002 |pmid=19944188}}</ref>

== References == {{Reflist|32em|refs= <ref name=ShortVahtera2017>{{Cite journal |last=Short |first=Megan |last2=Vahtera |first2=Varpu |date=2017-11-10 |title=Phylogenetic relationships of millipedes in the subclass Penicillata (Diplopoda) with a key to the genera |url=https://doi.org/10.1080/00222933.2017.1380241 |journal=Journal of Natural History |volume=51 |issue=41-42 |pages=2443–2461 |doi=10.1080/00222933.2017.1380241 |issn=0022-2933}}</ref> <ref name=MilliBase2025>{{Cite web |title=MilliBase - Polyxenida |url=https://www.millibase.org/aphia.php?p=taxdetails&id=387333 |access-date=2025-12-06 |website=www.millibase.org |language=en}}</ref> }}

== External links == {{Portal|Arthropods}} *{{Commons category-inline}} *{{Wikispecies-inline}} *{{EOL}} * {{usurped|1=[https://web.archive.org/web/20081013122503/http://www.nadiplochilo.com/opolyxenida.html Photos of Polyxenida]}}

Category:Polyxenida Category:Millipede orders Category:Taxa named by Karl Wilhelm Verhoeff