Editing Chaetognatha (section)

==Genetics==
===Mitochondrial genome===
The [[mtDNA]] of the arrow worm ''[[Spadella cephaloptera]]'' has been sequenced in 2004, and at the time it was the smallest metazoan mitochondrial genome known, being 11,905 base pairs long<ref name="Papillon2004"/> (it has now been surpassed by the mitchondrial genome of the [[ctenophore]] ''Mnemiopsis leidyi'', which is 10,326 bp long).<ref>{{cite journal |doi=10.3390/life11070663 |doi-access=free |title=Mitochondrial Genomic Landscape: A Portrait of the Mitochondrial Genome 40 Years after the First Complete Sequence |date=2021 |last1=Formaggioni |first1=Alessandro |last2=Luchetti |first2=Andrea |last3=Plazzi |first3=Federico |journal=Life |volume=11 |issue=7 |page=663 |pmid=34357035 |pmc=8303319 |bibcode=2021Life...11..663F }}</ref> All mitochondrial [[tRNA]] genes are absent. The [[MT-ATP8]] and [[MT-ATP6]] genes are also missing.<ref name="Papillon2004"/> The [[mtDNA]] of ''[[Paraspadella gotoi]]'', also sequenced in 2004, is even smaller (11,403 bp) and it shows a similar pattern, lacking 21 of the 22 usually present tRNA genes and featuring only 14 of the 37 genes normally present. <ref name="Helfenbein2004">{{cite journal |doi=10.1073/pnas.0400941101 |title=The mitochondrial genome of ''Paraspadella gotoi'' is highly reduced and reveals that chaetognaths are a sister group to protostomes |date=2004 |last1=Helfenbein |first1=Kevin G. |last2=Fourcade |first2=H. Matthew |last3=Vanjani |first3=Rohit G. |last4=Boore |first4=Jeffrey L. |journal=Proceedings of the National Academy of Sciences |volume=101 |issue=29 |pages=10639–10643 |pmid=15249679 |pmc=489987 |doi-access=free |bibcode=2004PNAS..10110639H }}</ref> 

Chaetognaths show a unique mitochondrial genomic diversity within individual of the same species.<ref name="Marletaz2017">{{cite journal |doi=10.1093/gbe/evx090 |title=Extreme Mitogenomic Variation in Natural Populations of Chaetognaths |date=2017 |last1=Marlétaz |first1=Ferdinand |last2=Le Parco |first2=Yannick |last3=Liu |first3=Shenglin |last4=Peijnenburg |first4=Katja TCA |journal=Genome Biology and Evolution |volume=9 |issue=6 |pages=1374–1384 |pmid=28854623 |pmc=5470650 }}</ref>