View source for Biology:Entognatha

{{Short description|Class of wingless and ametabolous arthropods}}
{{Paraphyletic group|auto=yes
| image = Protura specimen (Acerentomon species) micrograph.jpg
| image_caption = [[Biology:Protura|Protura]]n specimen (''Acerentomon'' sp.)
| display_parents = 2
| taxon = Entognatha
| authority = 
| includes =
*[[Biology:Diplura|Diplura]] (two-pronged bristletails)
*Collembola (springtails)
*[[Biology:Protura|Protura]] (coneheads)
| excludes = [[Biology:Insecta|Insecta]] (insects)
}}
[[File:Two-pronged Bristletail (Diplura) (10353381334).jpg|thumb|{{center|'''Diplura''', a Two-pronged Bristletail &mdash; not closely related to three-pronged bristletails in the Archaeognatha}} ]]

[[File:Katianna oceanica (13913339330).jpg|thumb|{{center|Collembola, family [[Biology:Sminthuridae|Sminthuridae]]}}]]
The '''Entognatha''' are a [[Biology:Class|class]] of wingless and [[Biology:Ametabolism|ametabolous]] [[Biology:Arthropod|arthropod]]s, which, together with the [[Biology:Insect|insect]]s, makes up the subphylum [[Biology:Hexapoda|Hexapoda]].<ref name="Grimaldi">{{cite book |author=David A. Grimaldi & [[Biography:Michael S. Engel|Michael S. Engel]] |year=2005 |title=Evolution of the Insects |publisher={{wipe|Cambridge University Press}} |isbn=978-0-521-82149-0 |chapter=Arthropods and the origin of insects |pages=93–118 |chapter-url=https://books.google.com/books?id=Ql6Jl6wKb88C&pg=PA111}}</ref><ref name="Gullan">{{cite book |author=P. J. Gullan, Peter Cranston |year=2010 |title=The Insects: an Outline of Entomology |edition=4th |publisher=John Wiley and Sons |isbn=978-1-4443-3036-6 |chapter=Insect systematics: phylogeny and classification |pages=189–222 |chapter-url=https://books.google.com/books?id=S7yGZasJ7nEC&pg=PA201}}</ref> Their [[Biology:Arthropod mouthparts|mouthparts]] are entognathous, meaning that they are retracted within the head, unlike the insects.<ref name="Grimaldi"/> Entognatha are apterous, meaning that they lack [[Biology:Insect wing|wings]]. The class contains three [[Biology:Order|orders]]: Collembola ([[Biology:Springtail|springtail]]s, 9000 species),<ref>{{cite journal | pmc=7365838 | year=2020 | last1=Ospina-Sánchez | first1=C. M. | last2=Soto-Adames | first2=F. N. | last3=González | first3=G. | title=Checklist and distribution of Collembola from Greater Puerto Rico | journal=Biodiversity Data Journal | volume=8 | pages=e52054 | doi=10.3897/BDJ.8.e52054 | pmid=32733139 | doi-access=free }}</ref> [[Biology:Diplura|Diplura]] (“two-tail”, 1000 species)<ref>{{Cite journal |doi=10.1111/icad.12480 |doi-access=free|title=Diversity, ecology, distribution and biogeography of Diplura |year=2021 |last1=Sendra |first1=Alberto |last2=Jiménez‐Valverde |first2=Alberto |last3=Selfa |first3=Jesús |last4=Reboleira |first4=Ana Sofia P. S. |journal=Insect Conservation and Diversity |volume=14 |issue=4 |pages=415–425 |hdl=10550/82616 |hdl-access=free }}</ref> and [[Biology:Protura|Protura]] (“first-tail”, 800 species).<ref>{{cite journal | pmc=6045683 | year=2018 | last1=Galli | first1=L. | last2=Shrubovych | first2=J. | last3=Bu | first3=Y. | last4=Zinni | first4=M. | title=Genera of the Protura of the World: Diagnosis, distribution, and key | journal=ZooKeys | issue=772 | pages=1–45 | doi=10.3897/zookeys.772.24410 | pmid=30018507 | doi-access=free }}</ref><ref name="Grimaldi"/><ref name="Gullan"/> These three groups were historically united with the now-obsolete order [[Biology:Thysanura|Thysanura]] to form the class [[Biology:Apterygota|Apterygota]], but it has since been recognized that the hexapodous condition of these animals has evolved independently from that of insects, and independently ''within'' each order.<ref>{{cite book |author=Alessandro Minelli |year=2009 |title=Perspectives in Animal Phylogeny and Evolution |publisher=[[Organization:Oxford University Press|Oxford University Press]] |isbn=978-0-19-856620-5 |chapter=A gallery of the major bilaterian clades |pages=71–109 |chapter-url=https://books.google.com/books?id=ood5LEkVTxcC&pg=PA101}}</ref> The orders might not be closely related, and Entognatha is now considered to be a paraphyletic group.<ref name="Gullan"/>

==Morphology==
These minute [[Biology:Arthropod|arthropod]]s are apterous, unlike some <!-- 'other' - No, as these aren't insects -->orders of insects that have lost their [[Biology:Insect wing|wings]] secondarily (but are derived from winged ancestors). Their mouthparts are enclosed within a pouch in the head capsule, called the gnathal pouch, so only the tips of the mandibles and maxillae are exposed beyond the cavity.<ref name="Grimaldi"/> This pouch is created in the embryo by a flap or lateral head sclerite near the mouth on each side of the head which fuses with the labium.<ref name="Grimaldi"/> Other differences with insects are that each [[Biology:Antenna|antennal]] segment is musculated; in insects, only the two basal segments are. Sperm transfer is always indirect, and there is an [[Biology:Ovipositor|ovipositor]] in the females. Of the three orders, only collembolans possess eyes;<ref name="Gullan"/> nevertheless, many collembolans are blind, and even when [[Biology:Compound eye|compound eye]]s are present, there are no more than eight ommatidia.

*Collembolans have a ventral tube termed a collophore on the first abdominal segment. The collophore is involved in moisture absorption. On the third abdominal segment is the retinaculum that holds the furcula. The furcula is the "spring" for which the Collembola are given the name springtails.
*Proturans, sometimes referred to as "coneheads", do not have eyes or antennae. They possess a [[Biology:Telson|telson]] and abdominal styli thought to be vestigial legs.
*Diplurans have a pair of caudal [[Biology:Cercus|cerci]], from which their name, meaning "two-tailed", is derived. They also possess abdominal styli.

==References==
{{Reflist|32em}}

{{Arthropods}}
{{Taxonbar|from=Q623286}}

[[Category:Entognatha| ]]
[[Category:Arthropod classes]]
[[Category:Paraphyletic groups]]

{{Sourceattribution|Entognatha}}