Gnathobase

Gnathobases of a horseshoe crab, with the chelicerae on the left

Gnathobases (from Ancient Greek γνάθος (gnáthos) 'jaw' and βᾰ́σῐς (básis) '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.

Gnathobases are present in extant and extinct arthropods, though only horseshoe crabs today have a well developed series of gnathobases along their limbs.

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"). True gnathobases are absent in arachnids.

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.

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 (sing. chilarium), a pair of reduced appendages that prevent food from escaping.

Other chelicerates

External videos
video icon Animated 3D model of Habelia moving its gnathobases
Diagram of the extinct Cambrian stem-chelicerate Habelia, showing the gnathobases (labeled g) on the underside of the head
Restoration of the underside of the head of Habelia, prominently showing the gnathobases running along the midline

Gnathobases are also found in other groups of chelicerates, such as in the mandible-like basipods of Habelia and Mollisonia.

Artiopoda including Trilobita

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, as well as others like Sidneyia.

In Mandibulata

Mandibles, the eponymous appendages of the Mandibulata, may have originated from thoracic legs possessing gnathobasic endites.

Crustacea

Crustaceans including copepods have gnathobases on the mandible.

See also

References

  1. ↑ Allaby, Michael (2009). "gnathobase". A Dictionary of Zoology. Oxford University Press. doi:10.1093/acref/9780199233410.001.0001. ISBN 978-0-19-923341-0.
  2. 1 2 3 Bicknell, Russell D. C.; Ledogar, Justin A.; Wroe, Stephen; Gutzler, Benjamin C.; Watson, Winsor H.; Paterson, John R. (2018-10-24). "Computational biomechanical analyses demonstrate similar shell-crushing abilities in modern and ancient arthropods". Proceedings of the Royal Society B: Biological Sciences. 285 (1889). 20181935. doi:10.1098/rspb.2018.1935. ISSN 0962-8452. PMC 6234888. PMID 30355715.
  3. ↑ Haug, Carolin (2020-08-13). "The evolution of feeding within Euchelicerata: data from the fossil groups Eurypterida and Trigonotarbida illustrate possible evolutionary pathways". PeerJ. 8 e9696. doi:10.7717/peerj.9696. ISSN 2167-8359. S2CID 225384853.
  4. ↑ Howard, Richard J.; Puttick, Mark N.; Edgecombe, Gregory D.; Lozano-Fernandez, Jesus (November 2020). "Arachnid monophyly: Morphological, palaeontological and molecular support for a single terrestrialization within Chelicerata". Arthropod Structure & Development. 59 100997. Bibcode:2020ArtSD..5900997H. doi:10.1016/j.asd.2020.100997. PMID 33039753.
  5. ↑ Lamsdell, James C.; Gunderson, Gerald O.; Meyer, Ronald C. (2019-01-08). "A common arthropod from the Late Ordovician Big Hill Lagerstätte (Michigan) reveals an unexpected ecological diversity within Chasmataspidida". BMC Evolutionary Biology. 19 (1): 8. Bibcode:2019BMCEE..19....8L. doi:10.1186/s12862-018-1329-4. ISSN 1471-2148. PMC 6325806. PMID 30621579.
  6. ↑ Bicknell, Russell D.C; Paterson, John R; Caron, Jean-Bernard; Skovsted, Christian B (2017). "The gnathobasic spine microstructure of recent and Silurian chelicerates and the Cambrian artiopodan Sidneyia: Functional and evolutionary implications". Arthropod Structure & Development. 47 (1): 12–24. doi:10.1016/j.asd.2017.12.001. PMID 29221679. S2CID 46830374.
  7. ↑ Aria, Cédric; Caron, Jean-Bernard (2019). "A middle Cambrian arthropod with chelicerae and proto-book gills". Nature. 573 (7775): 586–589. Bibcode:2019Natur.573..586A. doi:10.1038/s41586-019-1525-4. ISSN 1476-4687. PMID 31511691.
  8. ↑ Losso, Sarah R.; Nanglu, Karma; Weyland, Walker C.; Ortega-Hernández, Javier (2025-08-04). "Quantification of leg mobility in the Burgess Shale Olenoides serratus indicates functional differences between trilobite and xiphosuran appendages". BMC Biology. 23 (1) 238. doi:10.1186/s12915-025-02335-3. ISSN 1741-7007. PMC 12320380. PMID 40754578.
  9. ↑ Izquierdo-López, Alejandro; Caron, Jean-Bernard (2022). "The problematic Cambrian arthropod Tuzoia and the origin of mandibulates revisited". Royal Society Open Science. 9 (12) 220933. Bibcode:2022RSOS....920933I. doi:10.1098/rsos.220933. ISSN 2054-5703. PMC 9727825. PMID 36483757.
  10. ↑ Michels, Jan; Gorb, Stanislav N (2015-03-06). "Mandibular gnathobases of marine planktonic copepods – feeding tools with complex micro- and nanoscale composite architectures". Beilstein Journal of Nanotechnology. 6: 674–685. doi:10.3762/bjnano.6.68. ISSN 2190-4286. PMC 4362211. PMID 25821707.