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Gnathifera (clade)

Gnathifera (from the Greek gnáthos, “jaw”, and the Latin -fera, “bearing”) is a clade of generally small spiralians characterized by complex jaws made of chitin. It comprises the phyla Gnathostomulida, Rotifera, Micrognathozoa, and Chaetognatha.[1] It may also include the Cycliophora.[2]

Gnathifera
Temporal range: FortunianRecent
Scientific classification e
Kingdom: Animalia
(unranked): Spiralia
Clade: Gnathifera
Ahlrichs, 1995
Phyla

Gnathiferans include some of the most abundant phyla. Rotifers are among the most diverse and abundant freshwater animals and chaetognaths are among the most abundant marine plankton.[3][4]

DescriptionEdit

The most distinctive characteristic of gnathiferans is the presence of complex sclerotized mouthparts made of chitin.[1]

In most gnathiferans, the anus opens on the dorsal surface of the animal.[5][6][7] In micrognathozoans and gnathostomulids, the anus is transient and only forms during defecation.[6][7] Unlike other gnathiferans, in chaetognaths and Amiskwia the anus is located on the ventral surface in a subterminal position.[8][9]

DevelopmentEdit

All known gnathiferans are direct developers.[10] Though gnathiferans are included in Spiralia, rotifers and chaetognaths do not exhibit spiral cleavage.[10][1] Little is known of the development of micrognathozoans.[10] The development of gnathostomulids is poorly known, but they appear to exhibit spiral cleavage.[10][1]

ClassificationEdit

Spiralia
Gnathifera

Gnathostomulida

Micrognathozoa

Chaetognatha

Rotifera

Seisonida

Acanthocephala

Bdelloidea

Monogononta

Platytrochozoa

Summary of relationships of gnathiferans in recent studies, with disputed relationships represented as polytomies[1][5][11][12][13]

Gnathifera is a member of Spiralia. It is the sister taxon of a clade comprising all other spiralians.[1][12] Before the cladistic era, most gnathiferans were regarded as aschelminths, a grouping now recognized as polyphyletic.

Chaetognaths exhibit numerous morphological similarities to rotifers, suggesting that they may be sister taxa.[5][11] However, based on molecular data, micrognathozoans may be more closely related to rotifers than chaetognaths.[1]

Rotifera comprises four subclades: Seisonida, Acanthocephala, Bdelloidea, and Monogononta. Acanthocephalans were traditionally excluded from Rotifera, but it is now known that rotifers are paraphyletic without including acanthocephalans. Some taxonomists call the clade of rotifers including acanthocephalans Syndermata, but others continue to use Rotifera and regard acanthocephalans as rotifers.[12] Numerous hypotheses of rotifer interrelationships exist.[12][13]

The engimatic phylum Cycliophora may belong to Gnathifera, but other studies suggest that it is more closely related to the Entoprocta.[2]

Fossil recordEdit

The fossil record of gnathiferans is poor. There are no known fossil gnathostomulids.[14] Fossils of the extant rotifer genus Habrotrocha are known from Dominican amber dating to the late Eocene, but rotifers are otherwise only known from the Holocene.[15][16] By contrast, the chaetognath fossil record, while still patchy, includes numerous Paleozoic specimens.[17] Protoconodonts are stem-group chaetognaths.[18] The earliest protoconodonts date to the Fortunian age of the Cambrian, and are among the oldest known bilaterians.[19] The enigmatic Cambrian taxon Amiskwia is a gnathiferan and may also be a stem-group chaetognath.[5][8] The Cambrian ectoparasite Inquicus appears to be a gnathiferan.[5]

HistoryEdit

Gnathifera was named in 1995 to unite gnathostomulids and rotifers. Micrognathozoans were soon added to this grouping. Chaetognaths, long considered a distinct lineage with no close relatives, were identified as gnathiferans in 2019.[1]

A similar grouping, Acanthognatha, was suggested in 1998 to unite gastrotrichs with gnathostomulids and rotifers.[20] However, gastrotrichs are more closely related to lophotrochozoans than gnathiferans.[12][1]

ReferencesEdit

  1. ^ a b c d e f g h i Marlétaz, Ferdinand; Peijnenburg, Katja T. C. A.; Goto, Taichiro; Satoh, Noriyuki; Rokhsar, Daniel S. (2019). "A new spiralian phylogeny places the enigmatic arrow worms among gnathiferans". Current Biology. 29 (2): 312–318.e3. doi:10.1016/j.cub.2018.11.042. PMID 30639106.
  2. ^ a b Kristensen, Reinhardt Møbjerg (2002). "An Introduction to Loricifera, Cycliophora, and Micrognathozoa". Integrative and Comparative Biology. 42 (3): 641–651. doi:10.1093/icb/42.3.641.
  3. ^ Suga K, Mark Welch D, Tanaka Y, Sakakura Y, Hagiwara A (2007). "Analysis of expressed sequence tags of the cyclically parthenogenetic rotifer Brachionus plicatilis". PLoS ONE. 2 (7): e671. doi:10.1371/journal.pone.0000671. PMC 1925144. PMID 17668053.
  4. ^ Longhurst, Alan R. (1985). "The structure and evolution of plankton communities". Progress in Ocenography. 15: 1–35. doi:10.1016/0079-6611(85)90036-9.
  5. ^ a b c d e Vinther, Jakob; Parry, Luke A. (2019). "Bilateral jaw elements in Amiskwia sagittiformis bridge the morphological gap between gnathiferans and chaetognaths". Current Biology. 29 (5): 881–888.e1. doi:10.1016/j.cub.2019.01.052. PMID 30799238.
  6. ^ a b Knauss, Elizabeth B. (1979). "Indication of an anal pore in Gnathostomulida". Zoologica Scripta. 8: 181–186. doi:10.1111/j.1463-6409.1979.tb00630.x.
  7. ^ a b Kristensen, Reinhardt Møbjerg; Funch, Peter (2000). "Micrognathozoa: a new class with complicated jaws like those of Rotifera and Gnathostomulida". Journal of Morphology. 246: 1–49. doi:10.1002/1097-4687(200010)246:1<1::AID-JMOR1>3.0.CO;2-D. PMID 11015715.
  8. ^ a b Caron, Jean-Bernard; Cheung, Brittany (2019). "Amiskwia is a large Cambrian gnathiferan with complex gnathostomulid-like jaws". Communications Biology. 2. doi:10.1038/s42003-019-0388-4.
  9. ^ "Morphology and ultrastructure of the gut in Spadella cephaloptera (Chaetognatha)". Journal of Morphology. 228: 27–44. 1996. doi:10.1002/(SICI)1097-4687(199604)228:1<27::AID-JMOR3>3.0.CO;2-M.
  10. ^ a b c d Hejnol, Andreas. "Gnathifera". In Wanninger, A. (ed.). Evolutionary Developmental Biology of Invertebrates 2: Lophotrochozoa (Spiralia). Springer. doi:10.1007/978-3-7091-1871-9_1.
  11. ^ a b Fröbius, Andreas C.; Funch, Peter (2017). "Rotiferan Hox genes give new insights into the evolution of metazoan bodyplans". Nature Communications. 8 (1): 9. doi:10.1038/s41467-017-00020-w. PMC 5431905. PMID 28377584.
  12. ^ a b c d e Laumer, Christopher E.; Bekkouche, Nicolas; Kerbl, Alexandra; Goetz, Freya; Neves, Ricardo C.; Sørensen, Martin V.; Kristensen, Reinhardt M.; Hejnol, Andreas; Dunn, Casey W.; Giribet, Gonzalo; Worsaae, Katrine (2015). "Spiralian phylogeny informs the evolution of microscopic lineages". Current Biology. 25: 2000–2006. doi:10.1016/j.cub.2015.06.068.
  13. ^ a b "Phylogeny of Syndermata (syn. Rotifera): Mitochondrial gene order verifies epizoic Seisonidea as sister to endoparasitic Acanthocephala within monophyletic Hemirotifera". Molecular Phylogenetics and Evolution. 96: 79–92. 2016. doi:10.1016/j.ympev.2015.11.017.
  14. ^ Piper, Ross (2013). Animal Earth: The Amazing Diversity of Living Creatures. Thames & Hudson.
  15. ^ Poinar, G. O.; Ricci, C. (1992). "Bdelloid rotifers in Dominican amber: evidence for parthenogenetic continuity". Experientia. 48: 408–410. doi:10.1007/bf01923444.
  16. ^ Waggoner, B. M.; Poinar, G. O. (1993). "Fossil habrotrochid rotifers in Dominican amber". Experientia. 49: 354–357. doi:10.1007/bf01923421.
  17. ^ Vannier, J.; Steiner, M.; Renvoisé, E.; Hu, S.-X.; Casanova, J.-P. (2007). "Early Cambrian origin of modern food webs: evidence from predator arrow worms". Proceedings of the Royal Society B. 274: 627–633. doi:10.1098/rspb.2006.3761. PMC 2197202.
  18. ^ Szaniawski, Hubert (2002). "New evidence for the protoconodont origin of chaetognaths". Acta Palaeontologica Polonica. 47 (3): 405–419.
  19. ^ Kouchinsky, Artem; Bengtson, Stefan; Runnegar, Bruce; Skovsted, Christian; Steiner, Michael; Vendrasco, Michael (2011). "Chronology of early Cambrian biomineralization". Geological Magazine. 149 (2): 221–251. doi:10.1017/S0016756811000720.
  20. ^ Cavalier-Smith, T. (1998). "A revised six-kingdom system of life". Biological Reviews. 73 (3): 203–266. doi:10.1111/j.1469-185X.1998.tb00030.x. PMID 9809012.