# Polydesmus progressus

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{{Short description|Species of millipede}}
{{Speciesbox
|image =
|image_caption =
| status =
| status_system =
| status_ref =
| genus = Polydesmus
| species = progressus
| authority = [Brölemann](/source/Henri_W._Br%C3%B6lemann), 1900
| synonyms =
* ''Perapolydesmus progressus'' <small>(Brölemann, 1900)</small>
}}
'''''Polydesmus progressus''''' is a [species](/source/species) of [flat-backed millipede](/source/flat-backed_millipede) in the [family](/source/Family_(taxonomy)) [Polydesmidae](/source/Polydesmidae).<ref name=":1">{{Cite web |last1=Sierwald |first1=P. |last2=Decker |first2=P. |last3=Spelda |first3=J. |title=MilliBase – Polydesmus progressus Brölemann, 1900 |url=https://www.millibase.org/aphia.php?p=taxdetails&id=950008 |access-date=2025-03-25 |website=www.millibase.org}}</ref><ref>{{Cite web |title=Polydesmus progressus Brölemann, 1900 {{!}} COL |url=https://www.catalogueoflife.org/data/taxon/856J2 |access-date=2025-03-26 |website=www.catalogueoflife.org}}</ref> This species is found in [France](/source/France), usually in caves.<ref name=":5">{{Cite book |last=Attems |first=Karl |url=https://www.degruyter.com/document/doi/10.1515/9783111609645/html |title=Lieferung 70 Polydesmoidea III: Fam. Ploydesmidae, Vanhoeffeniidae, Cryptodesmidae, Oniscodesmidae, Sphaeretrichopidae, Peridontodesmidae, Rhachidesmidae, Macellolophidae, Pandirodesmidae |date=1940 |publisher=De Gruyter |isbn=978-3-11-160964-5 |pages=147–149 |language=de |doi=10.1515/9783111609645}}</ref><ref name=":2">{{Cite journal |last=Brölemann |first=H.W. |date=1910 |title=Biospeologica. XVII. Symphyles, Pselaphognathes, Polydesmoides et Lysiopetaloides (Myriapodes) (première série) |url=https://www.biodiversitylibrary.org/item/28434#page/526/mode/1up |journal=Archives de zoologie expérimentale et générale |series=5e série |language=French |volume=5 |issue=7 |pages=339-378 [342-345] |via=Biodiversity Heritage Library}}</ref> This [millipede](/source/millipede) exhibits [sexual dimorphism](/source/sexual_dimorphism) in segment number: Whereas adult females of this species feature the 20 segments (counting the collum as the first segment and the [telson](/source/telson) as the last) usually observed on the [order](/source/Order_(biology)) [Polydesmida](/source/Polydesmida), the adult males feature only 19 segments.<ref name=":0">{{Cite journal |last=Brölemann |first=H.W. |date=1900 |title=Myriapodes cavernicoles descriptions d'espèces nouvelles |url=https://www.biodiversitylibrary.org/page/8249607#page/88/mode/1up |journal=Annales de la Société entomologique de France |language=French |volume=69 |issue=1 |pages=73-81 [78-80] |via=Biodiversity Heritage Library}}</ref><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 [147, 149–150] |doi=10.1111/j.1096-3642.1993.tb00305.x|url-access=subscription }}</ref>

== Discovery, distribution, and habitat ==
This species was first [described](/source/Species_description) in 1900 by the French [myriapodologist](/source/Myriapodology) [Henri W. Brölemann](/source/Henry_Wilfred_Brolemann). He based the original description of this species on specimens including each sex. These specimens were collected from three sites in southern France: the [Lombrives](/source/Lombrives) cave in [department](/source/Departments_of_France) of [Ariège](/source/Ari%C3%A8ge_(department)), the [Bétharram](/source/Grottes_de_B%C3%A9tharram) cave in what is now the department of [Pyrénées-Atlantiques](/source/Pyr%C3%A9n%C3%A9es-Atlantiques) (formerly Basses-Pyrénées), and the Lautaret cave in the department of [Ardèche](/source/Ard%C3%A8che).<ref name=":0" />

In 1910, Brölemann described a new [subspecies](/source/subspecies), which he named ''Polydesmus progressus beneharnensis'', found to be abundant in the Bétharram cave, and distinguished this subspecies from the more widespread subspecies he described in 1900, which he named ''Polydesmus progressus typica''. He distinguished these subspecies based on differences in the [gonopod](/source/gonopod)s in adult males after examining a large sample of additional specimens collected from dozens of sites in southern France. This sample included specimens of the more widespread subspecies collected from the [Gargas](/source/Caves_of_Gargas) cave in [Saint-Laurent-de-Neste](/source/Saint-Laurent-de-Neste) in the department of [Hautes-Pyrénées](/source/Hautes-Pyr%C3%A9n%C3%A9es), a cave in [Limoux](/source/Limoux) in the department of [Aude](/source/Aude), a cave in [Aspet](/source/Aspet%2C_Haute-Garonne) in department of [Haute-Garonne](/source/Haute-Garonne), and more than a dozen sites in the department of Ariège, including the [Niaux](/source/Cave_of_Niaux) cave in [Tarascon-sur-Ariège](/source/Tarascon-sur-Ari%C3%A8ge), three caves in [Foix](/source/Foix), three caves in [Lavelanet](/source/Lavelanet), a cave in [Tarascon-sur-Ariège](/source/Tarascon-sur-Ari%C3%A8ge), two underground rivers in [Varilhes](/source/Varilhes), a cave in [Labastide-de-Sérou](/source/La_Bastide-de-S%C3%A9rou), and a cave in [Oust](/source/Oust%2C_Ari%C3%A8ge).<ref name=":2" />

The more widespread subspecies has also been found living on the surface outside of caves. The French [zoologist](/source/Zoology) [Henri Ribaut](/source/Henri_Ribaut) reported this subspecies found at ground level in the department of Haute-Garonne. Other specimens have been collected from the soil surface in gardens and under trees in the [Gave de Pau](/source/Gave_de_Pau) valley in the department of Pyrénées-Atlantiques.<ref name=":2" />

== Taxonomy ==
In 1916, Brölemann proposed a new genus, ''Perapolydesmus'', to contain the species originally described as ''Polydesmus progressus'', which he designated as the [type species](/source/type_species).<ref name=":3">{{Cite journal |last=Brölemann |first=Henry W. |date=1916 |title=Essai de classification des Polydesmiens (Myriapodes) |url=https://www.biodiversitylibrary.org/page/8559505#page/647/mode/1up |journal=Annales de la Société entomologique de France |language=French |volume=84 |issue=4 |pages=523–608 [607] |via=Biodiversity Heritage Library}}</ref> In 1940, the Austrian [myriapodologist](/source/Myriapodology) [Carl Attems](/source/Carl_Attems) moved the species originally described in 1934 as ''[Polydesmus susatensis](/source/Polydesmus_susatensis)'' to the genus ''Perapolydesmus''.<ref name=":5" /> Authorities now deem ''Perapolydesmus'' to be a [junior synonym](/source/Synonym_(taxonomy)) of ''Polydesmus'', however, thereby returning both species to the genus in which they were originally placed.<ref name=":13">{{Cite web |last1=Sierwald |first1=P. |last2=Decker |first2=P. |last3=Spelda |first3=J. |title=MilliBase - Perapolydesmus Brölemann, 1916 |url=https://www.millibase.org/aphia.php?p=taxdetails&id=892283 |access-date=2025-03-25 |website=www.millibase.org}}</ref>

== Description ==
This species is small and white.<ref name=":5" /> The two subspecies of this species differ in average size: The average adult male of the more widespread subspecies can range from 4.5&nbsp;mm to 5.6&nbsp;mm in length and from 0.66 to 0.74&nbsp;mm in width, whereas the average adult female can range from 6.5&nbsp;mm to 7.6&nbsp;mm in length and from 0.8&nbsp;mm to 0.95&nbsp;mm in width. The Bétharram subspecies is smaller than typical for this species, with the average adult male measuring 4.5&nbsp;mm in length and 0.6 in width and the average adult female measuring 6.3&nbsp;mm in length and 0.8&nbsp;mm in width.<ref name=":2" />

The [antennae](/source/Antenna_(zoology)) are long and shaped like clubs, each slender at the base but with thicker fifth, sixth, and seventh segments.<ref name=":0" /> The sixth is the largest segment.<ref name=":0" /><ref name=":5" /> The head is wider than the collum, which is shaped like a semicircle.<ref name=":0" /><ref name=":3" /> The [paranota](/source/Tergum) are well developed and each feature three to five teeth on the lateral edges.<ref name=":0" /><ref name=":5" /> The [ozopore](/source/ozopore)s appear on segments 5, 7, 9, 10, 12, 13, and from 15 to the penultimate segment. The legs are fairly long and feature bristles.<ref name=":0" />

The adult female features 20 segments (including the telson) and 31 pairs of legs, whereas the adult male features only 19 segments and 28 pairs of walking legs,<ref name=":0" /> excluding the eighth leg pair, which become a pair of gonopods.<ref name=":12" /> Each gonopod features a distal element (telopodite) that divides into two slender branches.<ref name=":3" /> The inner branch is shorter and features a pad with a tuft of bristles just before the tip, and these bristles conceal the opening of the seminal groove. The outer branch is longer and ends in a curved point with a hooked tooth just before the tip.<ref name=":0" /><ref name=":5" />

The two subspecies can be distinguished based on features of these gonopods. For example, the hairy pad appears on a very prominent protruding [tubercle](/source/tubercle) in the Bétharram subspecies but not in the more widespread subspecies. Furthermore, the outer branch is much longer than the inner branch in the more widespread subspecies, but the inner branch is nearly as long as the outer branch in the Bétharram subspecies.<ref name=":5" /><ref name=":2" />

This species shares many traits with ''Polydesmus susatensis'', and Attems placed these two species together in the genus ''Perapolydesmus'' based on these shared traits. For example, both species lack pigment and feature only 19 segments in the adult male. Furthermore, in both species, the head is wider than the collum, the antennae are shaped like clubs, and each gonopod divides into two branches with a shorter seminal branch that features a hairy pad near the tip.<ref name=":5" />

These two species can be distinguished, however, based on other traits. For example, the two branches of the gonopod are divided at the base by a suture in ''P. susatensis'' but not in ''P. progressus''. Furthermore, the outer branch of the gonopod is more curved in ''P. susatensis'' than in ''P. progressus'', and ''P. susatensis'' is also a larger species, with the adult male reaching 12&nbsp;mm in length.<ref name=":5" />

== References ==
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{{taxonbar|from=Q6446626}}

Category:Polydesmida
Category:Millipedes of Europe
Category:Fauna of France
Category:Cave millipedes
Category:Taxa named by Henry Wilfred Brolemann
Category:Animals described in 1900

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Adapted from the Wikipedia article [Polydesmus progressus](https://en.wikipedia.org/wiki/Polydesmus_progressus) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Polydesmus_progressus?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.