Editing Chaetognatha (section)

==History==
The first known description of a chaetognath has been published by Dutch naturalist [[Martinus Slabber]] in the 1770s; he also coined the name "arrow worm".<ref name="Slabber1778">{{cite book |last1=Slabber |first1=Martinus |title=Natuurkundige Verlustigingen, Behelzende Microscopise Waarneemingen Van de in—En Uitlandse Water—En Land-Dieren |date=1778 |publisher=J. Bosch |location=Haarlem |pages=46–48 |url=https://books.google.com/books?id=f8rDmjs4abkC&pg=PA3}}</ref><ref name="Pauly2021"/> The zoologist [[Henri Marie Ducrotay de Blainville]] also briefly mentioned probable chaetognaths but he understood them as pelagic mollusks. The first description of a currently accepted species of chaetognath, ''[[Sagitta bipunctata]]'', is from 1827.<ref name="Quoy1827">Quoy, J.R.C.; Gaimard, J.P. "Observations Zoologiques Faites à Bord de l’Astrolabe, en Mai 1826, dans le Détroit de Gibraltar (suite et fin). Description des genres Biphore, Carinaire, Hyale, Flèche, Cléodore, Anatife et Briarée." ''Ann. Sci. Nat.'' 1827, 10, 225–239</ref><ref name="Pauly2021"/> Among the early zoologists describing arrow worms, there is [[Charles Darwin]], who took notes about them during the [[Second voyage of HMS Beagle|voyage of the ''Beagle'']] and in 1844 dedicated a paper to them.<ref name="Darwin1844">Darwin, C. "Observations on the Structure and Propagation of the Genus Sagitta." ''Ann. Mag. Nat. Hist.'' 1844, 13, 1–6.</ref> In the following year, [[August David Krohn]] published an early anatomical description of ''Sagitta bipunctata''.<ref name="Krohn1845">{{cite journal |doi=10.1080/037454809496523 |title=XXXI.— ''Anatomical and physiological observations on'' Sagitta bipunctata |date=1845 |last1=Krohn |first1=M.A. |journal=Annals and Magazine of Natural History |volume=16 |issue=106 |pages=289–304 |url=https://www.biodiversitylibrary.org/part/60372 }}</ref><ref name="Choo2022"/>

The term "chaetognath" has been coined in 1856 by [[Rudolf Leuckart]]. He was also the first to propose that the genus ''Sagitta'' belonged to a separate group: «At the moment, it seems most natural to regard the Sagittas as representatives of a small group of their own that makes the transition from the real annelids (first of all the lumbricines) to the nematodes, and may not be unsuitably named Chaetognathi.»<ref name="Leuckart1856">Leuckart, R. Nachträge und Berichtigungen zu dem ersten Bande von J. van Der Hoeven’s Handbuch der Zoologie. Eine Systematisch Geordnete Übersicht der Hauptsächlichste Neueren Leistungen:über die Zoologie der Wirbellosen Thiere; L. Voss: Leipzig, Germany, 1856. (In German)</ref><ref name="Pauly2021"/>

The modern [[systematics]] of Chaetognatha begins in 1911 with Ritter-Záhony<ref name="Ritter-Zahony1911">Ritter-Záhony R. (1911) "Revision der Chaetognathan." ''Deutsche Sudpolar Expedition 1901–1903''. Band 13, Zoologie 5. Hft. 1: 1–72.</ref><ref name="Choo2022"/> and is later consolidated by [[Takasi Tokioka]] in 1965<ref name="Tokioka1965">{{cite journal |doi=10.5134/175381 |title=The Taxonomical Outline of Chaetognatha |date=1965 |last1=Tokioka |first1=Takasi |journal=Publications of the Seto Marine Biological Laboratory |volume=12 |issue=5 |pages=335–357 |s2cid=81053929 |doi-access=free }}</ref><ref name="Pauly2021"/><ref name="Choo2022"/> and Robert Bieri in 1991.<ref name="Bieri1991">Bieri, Robert. "Systematics of the Chaetognatha." in ''The biology of chaetognaths'' (1991): 122–136.</ref> Tokioka introduced the orders [[Phragmophora]] and [[Aphragmophora]], and classified four families, six genera, for a total of 58 species – plus the extinct ''[[Amiskwia]]'', classified as a true primitive chaetognath in a separate class, Archisagittoidea.<ref name="Choo2022"/>

Chaetognaths were for a while considered as belonging or affine to the [[deuterostomes]], but suspects of their affinities among [[Spiralia]] or other protostomes were already present as early as 1986.<ref name="Papillon2004">{{cite journal |doi=10.1093/molbev/msh229 |title=Identification of Chaetognaths as Protostomes is Supported by the Analysis of Their Mitochondrial Genome |date=2004 |last1=Papillon |first1=Daniel |last2=Perez |first2=Yvan |last3=Caubit |first3=Xavier |last4=Le Parco |first4=Yannick |journal=Molecular Biology and Evolution |volume=21 |issue=11 |pages=2122–2129 |pmid=15306659 |doi-access=free }}</ref> Their affinities with protostomes were clarified in 2004 by sequencing and analysis of [[mtDNA]].<ref name="Papillon2004"/>