Symphyla

File:Scutigerella 63392733.jpg

Symphyla are small, cryptic myriapods without eyes and without pigment.{{cite web |url=http://www.environment.gov.au/biodiversity/abrs/online-resources/fauna/afd/taxa/SYMPHYLA |title=Class: Symphyla |work=Australian Faunal Directory |author=Penny Greenslade |date=2002-03-31 |publisher=Australian National University |url-status=dead |archive-url=https://web.archive.org/web/20150924052402/http://www.environment.gov.au/biodiversity/abrs/online-resources/fauna/afd/taxa/SYMPHYLA |archive-date=2015-09-24}} The body is soft and generally {{convert|2|to|10|mm|in|sigfig=1}} long, divided into two body regions: head and trunk. An exceptional size is reached in Hanseniella magna, which attains lengths of 12-13 mm (0.5 in). Scheller, U. (1996) https://onlinelibrary.wiley.com/doi/epdf/10.1111/j.1440-6055.1996.tb01391.x

The head has long, segmented antennae, a postantennal organ, three pairs of mouthparts: mandibles, the long first maxillae, and the second pair of maxillae which are fused to form the lower lip or labium of the mouth. The antennae serve as sense organs. Disc-like organs of Tömösváry, which probably sense vibrations, are attached to the base of the antennae, as they are in centipedes.{{cite book |author= Barnes, Robert D. |year=1982 |title= Invertebrate Zoology |publisher= Holt-Saunders International |location= Philadelphia, PA|pages= 817–818|isbn= 978-0-03-056747-6}}

The trunk comprises 14 segments, which is covered by microhairs on the lateral and ventral integument, and by a various number of dorsal tergal plates, from 15 in Scutigerella and Hanseniella, and up till 24 in Ribautiella, increasing the flexibility of the body. Legs are found on the first 12 segments. The 13th segment, which is fused with the 12th segment, bears a pair of spinnerets that resemble cerci, and the 14th segment has a pair of long sensory hairs (trichobothria). Around the anal opening there is a small telson.[https://books.google.no/books?id=x7vtCAAAQBAJ&pg=PA229&dq=Symphyla+spinnerets+paired+spin+glands+telson&hl=no&newbks=1&newbks_redir=0&sa=X&ved=2ahUKEwiH6OXgv4mJAxXwFRAIHR0fNEsQ6AF6BAgHEAI#v=onepage&q=Symphyla%20spinnerets%20paired%20spin%20glands%20telson&f=false Multicellular Animals: Volume II: The Phylogenetic System of the Metazoa][https://books.google.no/books?id=YLxJETTBCSsC&pg=PA182&dq=symphylans+twelve+leg-less+tergal+plates+24&hl=no&newbks=1&newbks_redir=0&sa=X&ved=2ahUKEwiBlJvZuYmJAxUFExAIHXfHK8MQ6AF6BAgKEAI#v=onepage&q=symphylans%20twelve%20leg-less%20tergal%20plates%2024&f=false The Invertebrates: A Synthesis][https://books.google.no/books?id=Hd4OEDo4gbwC&pg=PA367&dq=Symphyla+segments+vestigial+separated&hl=no&newbks=1&newbks_redir=0&sa=X&ved=2ahUKEwiK5u_vyoyJAxU6ExAIHXVFLZgQ6AF6BAgEEAI#v=onepage&q=Symphyla%20segments%20vestigial%20separated&f=false Biology of Arthropoda][https://books.google.no/books?id=sbBG4-G7arQC&pg=PA17&dq=symphyla+microhairs&hl=no&newbks=1&newbks_redir=0&sa=X&ved=2ahUKEwiOnYGay4yJAxVgLRAIHSjYBhgQ6AF6BAgKEAI#v=onepage&q=symphyla%20microhairs&f=false Intestinal Microorganisms of Termites and Other Invertebrates] Symphylans have been reported as living up to four years, and moult throughout their life. Immature individuals have six or seven pairs of legs on hatching, but they add an additional pair at each moult until the adult instar, which usually has twelve pairs of legs.{{cite web |title=Garden Symphylans |url=http://mint.ippc.orst.edu/symphid.htm |url-status=dead |archive-url=https://web.archive.org/web/20070803172418/http://mint.ippc.orst.edu/symphid.htm |archive-date=2007-08-03 |access-date=2007-07-02 |work=Integrated Pest Management on Peppermint-IPMP3.0 |publisher=Oregon State University}}{{cite web |title=Symphylans |url=https://encyclopediaofarkansas.net/entries/symphylans-14863/ |access-date=2021-05-29 |work=Entry: Symphylans |publisher=Encyclopedia of Arkansas}} This mode of development is known as hemianamorphosis.{{cite journal |last1=Fusco |first1=Giuseppe |date=December 2005 |title=Trunk segment numbers and sequential segmentation in myriapods. |url=https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1525-142X.2005.05064.x |journal=Evolution & Development |volume=7 |issue=6 |pages=608–617 |doi=10.1111/j.1525-142X.2005.05064.x |pmid=16336414 |s2cid=21401688 |access-date=25 August 2020|url-access=subscription }} Although most adult symphylans have twelve leg pairs, the first pair is absent or vestigial in some species (e.g., those in the genus Symphylella), so adults in some species have only eleven leg pairs.{{Cite book |last1=Szucsich |first1=Nikola |url=https://www.worldcat.org/oclc/812207443 |title=The Myriapoda. Volume 1 |last2=Scheller |first2=Ulf |publisher=Brill |year=2011 |isbn=978-90-04-18826-6 |editor-last=Minelli |editor-first=Alessandro |location=Leiden |pages=445–466 |chapter=Symphyla |oclc=812207443}}{{Citation |last1=Minelli |first1=Alessandro |title=Myriapods |date=2013-01-01 |url=https://www.sciencedirect.com/science/article/pii/B9780123847195002082 |pages=421–432 |editor-last=Levin |editor-first=Simon A |access-date=2022-02-28 |place=Waltham |publisher=Academic Press |language=en |doi=10.1016/b978-0-12-384719-5.00208-2 |isbn=978-0-12-384720-1 |last2=Golovatch |first2=Sergei I. |encyclopedia=Encyclopedia of Biodiversity (Second Edition)|url-access=subscription }} The species with 12 pairs are the only myriapods with actual legs on the first body segment, as the first pair of legs is modified into forcipules in centipedes, and in pauropods the segment is a reduced collum which bears ventrally a pair of small papillae, while in millipedes it's a collum without any appendages at all.[https://muse.jhu.edu/pub/255/oa_monograph/chapter/2413845 Textbook of Arthropod Anatomy]

Symphylans have several features linking them to early insects, such as a labium (fused second maxillae), an identical number of head segments and certain features of their legs. Each pair of legs is associated with an eversible structure, called a "coxal sac", that helps the animal absorb moisture, and a small stylus that may be sensory in function. Similar structures are found in the most primitive insects.File:Garden centipede (Scutigerella immaculata) life stages.jpg

Symphylans breathe through a pair of spiracles on the sides of their head, and are the only arthropods with spiracle openings on the head.[https://books.google.com/books?id=8ZnEDAAAQBAJ&dq=Symphylans+are+the+only+group+respiratory+openings+on+the+head&pg=PA206 BIOLOGICAL SCIENCE FUNDAMENTALS AND SYSTEMATICS - Volum III] These are connected to a system of tracheae that branch through the head and the first three segments of the body only.

The genital openings are located on the fourth body segment, but the animals do not copulate. Instead, the male deposits 150 to 450 packages of sperm, or spermatophores, on small stalks. The female then picks these up in her mouth, which contains special pouches for storing the sperm. She then lays her eggs, and attaches them to the sides of crevices or to moss or lichen with her mouth, smearing the sperm over them as she does so. The eggs are laid in groups of eight to twelve.

The spinnerets produce secretions that turn into a silk-like thread.{{Cite book |title=Arthropod Anatomy |chapter=X: The Symphyla |jstor=10.7591/j.ctvn1tb6g.14 |chapter-url=https://www.jstor.org/stable/pdf/10.7591/j.ctvn1tb6g.14.pdf }} One fossil species, Symphylella patrickmuelleri, was found preserved in Burmese Amber releasing long threads of silk.{{Cite journal |last1=Moritz |first1=Leif |last2=Wesener |first2=Thomas |date=2018-04-01 |title=Symphylella patrickmuelleri sp. nov. (Myriapoda: Symphyla): The oldest known Symphyla and first fossil record of Scolopendrellidae from Cretaceous Burmese amber |url=https://www.sciencedirect.com/science/article/pii/S0195667117304068 |journal=Cretaceous Research |language=en |volume=84 |pages=258–263 |doi=10.1016/j.cretres.2017.11.018 |bibcode=2018CrRes..84..258M |issn=0195-6671|url-access=subscription }} The silk plays a role in reproduction: the male deposits up to 450 spermatophores on stalks of silk.{{Cite web |title=Symphylans |url=https://encyclopediaofarkansas.net/entries/symphylans-14863/ |access-date=2023-05-02 |website=Encyclopedia of Arkansas |language=en-US |quote=For reproduction, males do not copulate with the female. Rather, they deposit 150 to 450 sperm packets (spermatophores) on top of short stalks of silk on the ground.}} Symphylans have also been reported releasing silk as a defense{{Citation |last=Schulze |first=L. |title=Structure, composition and properties of spun products |date=Jan 1975 |url=https://journals.co.za/doi/pdf/10.10520/AJA0000012_281}} and to suspend themselves in the air.

The symphylan fossil record is poorly known, with only five species recorded, all placed in living genera. The oldest records of both families are found in Burmese amber from the middle Cretaceous, approximately 99 million years ago. As a result, both families are thought to have diverged before the end of the Mesozoic Era.{{cite journal|last1=Moritz|first1=Leif|last2=Wesener|first2=Thomas|title=Symphylella patrickmuelleri sp. nov. (Myriapoda: Symphyla): The oldest known Symphyla and first fossil record of Scolopendrellidae from Cretaceous Burmese amber|journal=Cretaceous Research|volume=84|pages=258–263|date=2017|doi=10.1016/j.cretres.2017.11.018|bibcode=2018CrRes..84..258M }}{{cite book|first=Alessandro|last= Minelli|title=Treatise on Zoology - Anatomy, Taxonomy, Biology. The Myriapoda|url=https://books.google.com/books?id=IrWcS9fut1oC&pg=PA459|year=2011|publisher=BRILL|isbn=978-90-04-15611-1|page=459}}{{Cite journal|last1=Wesener|first1=Thomas|last2=Moritz|first2=Leif|date=2018-12-17|title=Checklist of the Myriapoda in Cretaceous Burmese amber and a correction of the Myriapoda identified by Zhang (2017)|journal=Check List|language=en|volume=14|issue=6|pages=1131–1140|doi=10.15560/14.6.1131|issn=1809-127X|doi-access=free|s2cid=92289899 }}

Despite their common name, morphological studies commonly place symphylans as more closely related to millipedes and pauropods than the centipedes, in the clade Progoneata.{{cite journal|last=Shear|first=William A.|author2=Edgecombe, Gregory D. |title=The geological record and phylogeny of the Myriapoda|journal=Arthropod Structure & Development|date=2010|volume=39|issue=2–3|pages=174–190|doi=10.1016/j.asd.2009.11.002|pmid=19944188|bibcode=2010ArtSD..39..174S }}{{cite journal|last=Gai|first=Yonghua|author2=Song, Daxiang |author3=Sun, Hongying |author4=Yang, Qun |author5= Zhou, Kaiya |title=The complete mitochondrial genome of Symphylella sp. (Myriapoda: Symphyla): Extensive gene order rearrangement and evidence in favor of Progoneata|journal=Molecular Phylogenetics and Evolution|date=2008|volume=49|issue=2|pages=574–585|doi=10.1016/j.ympev.2008.08.010|url=https://www.researchgate.net/publication/23248321 |pmid=18782622|bibcode=2008MolPE..49..574G }} Molecular studies have shown conflicting results, with some supporting the Progoneata clade, others aligning symphylans with centipedes or other arthropods, although some are weakly supported.{{cite journal|last=Regier|first=Jerome C.|author2=Wilson, Heather M. |author3=Shultz, Jeffrey W. |title=Phylogenetic analysis of Myriapoda using three nuclear protein-coding genes|journal=Molecular Phylogenetics and Evolution|date=2005|volume=34|issue=1|pages=147–158|doi=10.1016/j.ympev.2004.09.005|pmid=15579388|bibcode=2005MolPE..34..147R }} The clade is believed to be monophyletic.{{Cite journal |last1=Jin |first1=Ya-Li |last2=Godeiro |first2=Nerivania Nunes |last3=Bu |first3=Yun |date=2023-05-04 |title=Description of the first species of Scutigerella (Symphyla, Scutigerellidae) from China, with mitogenomic and genetic divergence analysis |url=https://zookeys.pensoft.net/article/99686/ |journal=ZooKeys |language=en |issue=1157 |pages=145–161 |doi=10.3897/zookeys.1157.99686 |pmid=37215163 |pmc=10193434 |issn=1313-2970 |doi-access=free |bibcode=2023ZooK.1157..145J }}

{{Reflist|32em}}

• {{cite book |author=C. A. Edwards |year=1990 |chapter=Symphyla |pages=891–910 |editor=Daniel L. Dindal |title=Soil Biology Guide |publisher=New York: Wiley |isbn=978-0-471-04551-9}}
• {{cite journal |author=U. Scheller |year=1961 |title=A review of the Australian Symphyla (Myriapoda) |journal=Australian Journal of Zoology |volume=9 |issue=1 |pages=140–171 |doi=10.1071/ZO9610140}}
• {{cite book |author=U. Scheller |year=1982 |chapter=Symphyla |pages=[https://archive.org/details/synopsisclassifi02park/page/688 688–689] |editor=Sybil P. Parker |title=Synopsis and Classification of Living Organisms |chapter-url=https://archive.org/details/synopsisclassifi02park |chapter-url-access=registration |publisher=New York: McGraw-Hill |isbn=978-0-07-079031-5}}
• {{cite journal |author=R. J. Tillyard |year=1930 |title=The evolution of the class Insecta |journal=Papers and Proceedings of the Royal Society of Tasmania |volume=1930 |pages=1–89|doi=10.26749/IXAJ2535 |url=https://figshare.com/articles/journal_contribution/The_evolution_of_the_class_Insecta/24604155/1/files/43233978.pdf }}

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Category:Arthropod classes

Category:Taxa named by John A. Ryder