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<h2 id="morphology">Morphology</h2> <p>These minute <a href="/facts/Arthropod/JKJLTFzp">arthropods</a> are apterous, unlike some orders of insects that have lost their <a href="/facts/Insect_wing/e9v05xWY">wings</a> 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.<a class="footnote-ref" id="fnref:11" href="#fn:11"><sup>11</sup></a> 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.<a class="footnote-ref" id="fnref:12" href="#fn:12"><sup>12</sup></a> Other differences from insects are that each <a href="/facts/Antenna_(biology)/F0F9Eof9">antennal</a> segment is musculated; in insects, only the two basal segments are. Sperm transfer is always indirect, and there is an <a href="/facts/Ovipositor/7rFyPfgX">ovipositor</a> in the females. Of the three orders, only collembolans possess eyes;<a class="footnote-ref" id="fnref:13" href="#fn:13"><sup>13</sup></a> nevertheless, many collembolans are blind, and even when <a href="/facts/Compound_eye/yoRE9HWY">compound eyes</a> are present, there are no more than eight <a href="/facts/Ommatidia/T2jummw4">ommatidia</a>. </p> <ul><li>Collembolans have a ventral tube termed a <a href="/facts/Collophore/vrR7Irbw">collophore</a> on the first abdominal segment. The collophore is involved in moisture absorption. On the third abdominal segment is the retinaculum that holds the <a href="/facts/Furcula_(Collembola)/vYTmCRLL">furcula</a>. The furcula is the "spring" for which the Collembola are given the name springtails.</li> <li>Proturans, sometimes referred to as "coneheads", do not have eyes or antennae. They possess a <a href="/facts/Telson/71eFnSJb">telson</a> and abdominal styli thought to be vestigial legs.</li> <li>Diplurans have a pair of caudal <a href="/facts/Cercus/brurUKpK">cerci</a>, from which their name, meaning "two-tailed", is derived. They also possess abdominal styli.</li></ul> <ul> <li>Arthropods portal</li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>David A. Grimaldi & Michael S. Engel (2005). "Arthropods and the origin of insects". Evolution of the Insects. Cambridge University Press. pp. 93–118. ISBN 978-0-521-82149-0. <a href="978-0-521-82149-0" target="_blank">978-0-521-82149-0</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>P. J. Gullan, Peter Cranston (2010). "Insect systematics: phylogeny and classification". The Insects: An Outline of Entomology (4th ed.). John Wiley and Sons. pp. 189–222. ISBN 978-1-4443-3036-6. <a href="978-1-4443-3036-6" target="_blank">978-1-4443-3036-6</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>David A. Grimaldi & Michael S. Engel (2005). "Arthropods and the origin of insects". Evolution of the Insects. Cambridge University Press. pp. 93–118. ISBN 978-0-521-82149-0. <a href="978-0-521-82149-0" target="_blank">978-0-521-82149-0</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>Ospina-Sánchez, C. M.; Soto-Adames, F. N.; González, G. (2020). "Checklist and distribution of Collembola from Greater Puerto Rico". Biodiversity Data Journal. 8: e52054. doi:10.3897/BDJ.8.e52054. PMC 7365838. PMID 32733139. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7365838" target="_blank">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7365838</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>Sendra, Alberto; Jiménez-Valverde, Alberto; Selfa, Jesús; Reboleira, Ana Sofia P. S. (2021). "Diversity, ecology, distribution and biogeography of Diplura". Insect Conservation and Diversity. 14 (4): 415–425. doi:10.1111/icad.12480. hdl:10550/82616. <a href="https://doi.org/10.1111%2Ficad.12480" target="_blank">https://doi.org/10.1111%2Ficad.12480</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>Galli, L.; Shrubovych, J.; Bu, Y.; Zinni, M. (2018). "Genera of the Protura of the World: Diagnosis, Distribution, and Key". ZooKeys (772): 1–45. Bibcode:2018ZooK..772....1G. doi:10.3897/zookeys.772.24410. PMC 6045683. PMID 30018507. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6045683" target="_blank">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6045683</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>David A. Grimaldi & Michael S. Engel (2005). "Arthropods and the origin of insects". Evolution of the Insects. Cambridge University Press. pp. 93–118. ISBN 978-0-521-82149-0. <a href="978-0-521-82149-0" target="_blank">978-0-521-82149-0</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> <li id="fn:8"><p>P. J. Gullan, Peter Cranston (2010). "Insect systematics: phylogeny and classification". The Insects: An Outline of Entomology (4th ed.). John Wiley and Sons. pp. 189–222. ISBN 978-1-4443-3036-6. <a href="978-1-4443-3036-6" target="_blank">978-1-4443-3036-6</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li> <li id="fn:9"><p>Alessandro Minelli (2009). "A gallery of the major bilaterian clades". Perspectives in Animal Phylogeny and Evolution. Oxford University Press. pp. 71–109. ISBN 978-0-19-856620-5. <a href="978-0-19-856620-5" target="_blank">978-0-19-856620-5</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li> <li id="fn:10"><p>P. J. Gullan, Peter Cranston (2010). "Insect systematics: phylogeny and classification". The Insects: An Outline of Entomology (4th ed.). John Wiley and Sons. pp. 189–222. ISBN 978-1-4443-3036-6. <a href="978-1-4443-3036-6" target="_blank">978-1-4443-3036-6</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></p></li> <li id="fn:11"><p>David A. Grimaldi & Michael S. Engel (2005). "Arthropods and the origin of insects". Evolution of the Insects. Cambridge University Press. pp. 93–118. ISBN 978-0-521-82149-0. <a href="978-0-521-82149-0" target="_blank">978-0-521-82149-0</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></p></li> <li id="fn:12"><p>David A. Grimaldi & Michael S. Engel (2005). "Arthropods and the origin of insects". Evolution of the Insects. Cambridge University Press. pp. 93–118. ISBN 978-0-521-82149-0. <a href="978-0-521-82149-0" target="_blank">978-0-521-82149-0</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></p></li> <li id="fn:13"><p>P. J. Gullan, Peter Cranston (2010). "Insect systematics: phylogeny and classification". The Insects: An Outline of Entomology (4th ed.). John Wiley and Sons. pp. 189–222. ISBN 978-1-4443-3036-6. <a href="978-1-4443-3036-6" target="_blank">978-1-4443-3036-6</a> <a href="#fnref:13" class="footnote-back-ref">↩</a></p></li> </ol>