Gnathobase

[[File:Horseshoe_Crab_chelicerae_and_gnathobases.jpg|thumb|Gnathobases of a horseshoe crab, with the chelicerae on the left]]

'''Gnathobases''' ({{etymology|grc|''{{wikt-lang|grc|γνάθος}}'' ({{grc-transl|γνάθος}})|jaw||''{{wikt-lang|grc|βᾰ́σῐς}}'' ({{grc-transl|βᾰ́σῐς}})|base}}) are paired modified sections on the underside of the base of some arthropod limbs (specifically on the basipod/basipodite, the basalmost segment which attaches directly to the body), used for food processing. They typically feature hard sclerotised spines (endites), which serve a masticatory function such as crushing and shredding prey, and can also aid in transporting food towards the mouth.<ref>{{Cite book |last=Allaby |first=Michael |chapter=gnathobase |date=2009 |chapter-url-access=subscription |chapter-url=https://www.oxfordreference.com/display/10.1093/acref/9780199233410.001.0001/acref-9780199233410-e-3698 |title=A Dictionary of Zoology |publisher=Oxford University Press |doi=10.1093/acref/9780199233410.001.0001 |isbn=978-0-19-923341-0 |language=en}}</ref><ref name=":1">{{Cite journal |last1=Bicknell |first1=Russell D. C. |last2=Ledogar |first2=Justin A. |last3=Wroe |first3=Stephen |last4=Gutzler |first4=Benjamin C. |last5=Watson |first5=Winsor H. |last6=Paterson |first6=John R. |date=2018-10-24 |title=Computational biomechanical analyses demonstrate similar shell-crushing abilities in modern and ancient arthropods |journal=Proceedings of the Royal Society B: Biological Sciences |language=en |volume=285 |issue=1889 |at=20181935 |doi=10.1098/rspb.2018.1935 |doi-access=free |issn=0962-8452 |pmc=6234888 |pmid=30355715}}</ref>

Gnathobases are present in extant and extinct arthropods, though only horseshoe crabs today have a well developed series of gnathobases along their limbs.<ref name=":1" />

== In Chelicerata == Chelicerates have gnathobases that function in conjunction with chelicerae and in some taxa with other structures.

=== Arachnida === In arachnids have similar structures usually present in the coxae of the pedipalps (hence they are called "'''gnathocoxae'''").<ref name=":0">{{Cite journal |last=Haug |first=Carolin |date=2020-08-13 |title=The evolution of feeding within Euchelicerata: data from the fossil groups Eurypterida and Trigonotarbida illustrate possible evolutionary pathways |journal=PeerJ |language=en |volume=8 |article-number=e9696 |doi=10.7717/peerj.9696 |doi-access=free |s2cid=225384853 |issn=2167-8359}}</ref> True gnathobases are absent in arachnids.<ref>{{Cite journal |last1=Howard |first1=Richard J. |last2=Puttick |first2=Mark N. |last3=Edgecombe |first3=Gregory D. |last4=Lozano-Fernandez |first4=Jesus |date=November 2020 |title=Arachnid monophyly: Morphological, palaeontological and molecular support for a single terrestrialization within Chelicerata |url=https://linkinghub.elsevier.com/retrieve/pii/S1467803920301201 |journal=Arthropod Structure & Development |language=en |volume=59 |article-number=100997 |doi=10.1016/j.asd.2020.100997|pmid=33039753 |bibcode=2020ArtSD..5900997H |url-access=subscription }}</ref>

=== Eurypterida === In eurypterids both pedipalps and all walking legs (pairs of appendages II to VI) have the basipods with gnathobases that function together with the metastoma. This distribution occurs similarly in the related group Chasmataspidida.<ref>{{Cite journal |last1=Lamsdell |first1=James C. |last2=Gunderson |first2=Gerald O. |last3=Meyer |first3=Ronald C. |date=2019-01-08 |title=A common arthropod from the Late Ordovician Big Hill Lagerstätte (Michigan) reveals an unexpected ecological diversity within Chasmataspidida |journal=BMC Evolutionary Biology |volume=19 |issue=1 |page=8 |doi=10.1186/s12862-018-1329-4 |doi-access=free |issn=1471-2148 |pmc=6325806 |pmid=30621579 |bibcode=2019BMCEE..19....8L }}</ref>

=== Xiphosura === In xiphosurans including living horseshoe crabs, gnathobases are found on the basipods of the pedipalps and walking legs, similar to those of eurypterids. They function with chilaria ({{singular}} chilarium), a pair of reduced appendages that prevent food from escaping.<ref>{{cite journal |last1=Bicknell |first1=Russell D.C |last2=Paterson |first2=John R |last3=Caron |first3=Jean-Bernard |last4=Skovsted |first4=Christian B |year=2017 |title=The gnathobasic spine microstructure of recent and Silurian chelicerates and the Cambrian artiopodan Sidneyia: Functional and evolutionary implications |url=http://urn.kb.se/resolve?urn=urn:nbn:se:nrm:diva-2864 |journal=Arthropod Structure & Development |volume=47 |issue=1 |pages=12–24 |doi=10.1016/j.asd.2017.12.001 |pmid=29221679 |s2cid=46830374}}</ref> === Other chelicerates === {{External media|video1=[https://www.youtube.com/watch?v=RAo0TAteUmo Animated 3D model of ''Habelia'' moving its gnathobases]|width=236px|float=right|video2=|}}{{multiple image | align = center | total_width = 300 | image1 = Habelia diagram.jpg | alt1 = | image2 = 20191004 Habelia optata head.png | alt2 = | footer = | caption1 = Diagram of the extinct Cambrian stem-chelicerate ''Habelia'', showing the gnathobases (labeled g) on the underside of the head | caption2 = Restoration of the underside of the head of ''Habelia'', prominently showing the gnathobases running along the midline | direction = vertical }}

Gnathobases are also found in other groups of chelicerates, such as in the mandible-like basipods of ''Habelia'' and ''Mollisonia''.<ref>{{Cite journal |last1=Aria |first1=Cédric |last2=Caron |first2=Jean-Bernard |date=2019 |title=A middle Cambrian arthropod with chelicerae and proto-book gills |journal=Nature |language=en |volume=573 |issue=7775 |pages=586–589 |doi=10.1038/s41586-019-1525-4 |pmid=31511691 |bibcode=2019Natur.573..586A |issn=1476-4687}}</ref>

== Artiopoda including Trilobita == [[File:Bicknell et al. 2018 Sidneyia inexpectans.png|thumb|Reconstructed limb of extinct Cambrian artiopod ''Sidneyia inexpectans,'' showing spined gnathobase in green]] Gnathobases are known to occur in Artiopoda, including in trilobites, the most well-known artiopod group,<ref>{{Cite journal |last1=Losso |first1=Sarah R. |last2=Nanglu |first2=Karma |last3=Weyland |first3=Walker C. |last4=Ortega-Hernández |first4=Javier |date=2025-08-04 |title=Quantification of leg mobility in the Burgess Shale Olenoides serratus indicates functional differences between trilobite and xiphosuran appendages |journal=BMC Biology |language=en |volume=23 |issue=1 |article-number=238 |doi=10.1186/s12915-025-02335-3 |doi-access=free |issn=1741-7007 |pmc=12320380 |pmid=40754578}}</ref> as well as others like ''Sidneyia''.<ref name=":1" />

== In Mandibulata == Mandibles, the eponymous appendages of the Mandibulata, may have originated from thoracic legs possessing gnathobasic endites.<ref>{{Cite journal |last1=Izquierdo-López |first1=Alejandro |last2=Caron |first2=Jean-Bernard |date=2022 |title=The problematic Cambrian arthropod Tuzoia and the origin of mandibulates revisited |journal=Royal Society Open Science |language=en |volume=9 |issue=12 |article-number=220933 |doi=10.1098/rsos.220933 |doi-access=free |issn=2054-5703 |pmc=9727825 |pmid=36483757 |bibcode=2022RSOS....920933I }}</ref>

=== Crustacea === Crustaceans including copepods have gnathobases on the mandible.<ref>{{Cite journal |last1=Michels |first1=Jan |last2=Gorb |first2=Stanislav N |date=2015-03-06 |title=Mandibular gnathobases of marine planktonic copepods – feeding tools with complex micro- and nanoscale composite architectures |url=https://www.beilstein-journals.org/bjnano/articles/6/68 |journal=Beilstein Journal of Nanotechnology |language=en |volume=6 |pages=674–685 |doi=10.3762/bjnano.6.68 |issn=2190-4286 |pmc=4362211 |pmid=25821707}}</ref>

== See also ==

* Arthropod mouthparts

== References ==  {{reflist}} Category:Arthropod anatomy Category:Arthropod morphology