Editing Ctenophora (section)

===Fossil record===

{{Further| Ctenorhabdotus capulus| Fasciculus vesanus| Xanioascus canadensis| Archaeocydippida hunsrueckiana| Paleoctenophora brasseli}}

Because of their soft, gelatinous bodies, ctenophores are extremely rare as fossils, and fossils that have been interpreted as ctenophores have been found only in [[Lagerstätte]]n, places where the environment was exceptionally suited to the preservation of soft tissue. Until the mid-1990s, only two specimens good enough for analysis were known, both members of the crown group, from the early [[Devonian]] (Emsian) [[geologic timescale|period]]. Three additional putative species were then found in the [[Burgess Shale]] and other Canadian rocks of similar age, about {{ma|505}} in the mid-[[Cambrian]] period. All three lacked tentacles but had between 24–80&nbsp;comb rows, far more than the eight typical of living species. They also appear to have had internal organ-like structures unlike anything found in living ctenophores. One of the fossil species first reported in 1996 had a large mouth, apparently surrounded by a folded edge that may have been muscular.<ref name=Morris1996/> Evidence from China a year later suggests that such ctenophores were widespread in the Cambrian, but perhaps very different from modern species – for example one fossil's comb-rows were mounted on prominent vanes.<ref>{{cite journal |last=Conway Morris |first=S. |author-link=Simon Conway Morris |year=2003 |title=The Cambrian "explosion" of metazoans and molecular biology: Would Darwin be satisfied? |journal=[[International Journal of Developmental Biology]] |volume=47 |issue=7–8 |pages=505–515 |pmid=14756326 |url=http://www.ijdb.ehu.es/fullaccess/fulltext.03078/ft505.pdf |access-date=2009-02-14 |archive-url=https://web.archive.org/web/20091224184258/http://www.ijdb.ehu.es/fullaccess/fulltext.03078/ft505.pdf
 |archive-date=2009-12-24}}</ref> The youngest fossil of a species outside the crown group is ''[[Daihuoides]]'' from the late Devonian, which belongs to a basal group that had been assumed to have gone extinct more than 140 million years earlier.<ref>{{cite journal | last1=Klug | first1=Christian | last2=Kerr | first2=Johanne | last3=Lee | first3=Michael S.Y. | last4=Cloutier | first4=Richard | year=2021 | title=A late-surviving stem-ctenophore from the Late Devonian of Miguasha (Canada) | journal=[[Scientific Reports]] | volume=11 | issue=1 | page=19039 | pmid=34561497 | pmc=8463547 | bibcode=2021NatSR..1119039K | doi=10.1038/s41598-021-98362-5 }}</ref>

The Ediacaran ''[[Eoandromeda]]'' could putatively represent a comb jelly.<ref name=Tang2011>{{Cite journal | last1=Tang | first1=F. | last2=Bengtson | first2=S. | last3=Wang | first3=Y. | last4=Wang | first4=X.L. | last5=Yin | first5=C.Y. | date=20 September 2011 | title=Eoandromeda and the origin of Ctenophora | journal=[[Evolution & Development]] | volume=13 | issue=5 | pages=408–414 | doi=10.1111/j.1525-142X.2011.00499.x | pmid=23016902| s2cid=28369431 }}</ref> It has eightfold symmetry, with eight spiral arms resembling the comblike rows of a ctenophore. If it is indeed ctenophore, it places the group close to the origin of the Bilateria.<ref>{{cite news |last1=Maxmen |first1=Amy |date=7 September 2011 |title=Ancient sea jelly shakes evolutionary tree of animals |magazine=[[Scientific American]] |url=https://www.scientificamerican.com/article/ancient-sea-jelly-makes-tree/ |access-date=21 June 2018 }}</ref>
The early Cambrian [[Sessility (zoology)|sessile]] [[frond]]-like fossil ''[[Stromatoveris]]'', from China's [[Chengjiang fauna|Chengjiang]] lagerstätte and dated to about {{ma|515}}, is very similar to [[Vendobionta]] of the preceding [[Ediacaran]] period. De-Gan Shu, [[Simon Conway Morris]], ''et al.'' found on its branches what they considered rows of cilia, used for [[filter feeding]]. They suggested that ''Stromatoveris'' was an evolutionary "aunt" of ctenophores, and that ctenophores originated from sessile animals whose descendants became swimmers and changed the cilia from a feeding mechanism to a propulsion system.<ref>{{cite journal |last1=Shu |first1=D.-G. |last2=Conway Morris |author2-link=Simon Conway Morris |first2=S. |last3=Han |first3=J. |last4=Li |first4=Y. |last5=Zhang |first5=X.L. |last6=Hua |first6=H. |last7=Zhang |first7=Z.F. |last8=Liu |first8=JN |last9=Guo |first9=J.F. |last10=Yao |first10=Y. |last11=Yasui |first11=K. |display-authors=6 |title=Lower Cambrian vendobionts from China and early diploblast evolution |journal=[[Science (journal)|Science]] |date=5 May 2006 |volume=312 |issue=5774 |pages=731–734 |doi=10.1126/science.1124565 |pmid=16675697 |bibcode=2006Sci...312..731S |s2cid=1235914 }}</ref> Other Cambrian fossils that support the idea of ctenophores having evolved from sessile forms are ''[[Dinomischus]]'', ''[[Daihua]]'', ''[[Xianguangia]]'' and ''[[Siphusauctum]]'' which also lived on the seafloor, had organic skeletons and cilia-covered tentacles surrounding their mouth, which have been found by [[cladistics|cladistic]] analysis as members of the ctenophore [[stem-group]]<ref>{{cite journal |last1=Zhao |first1=Yang |last2=Vinther |first2=Jakob |last3=Parry |first3=Luke A. |last4=Wei |first4=Fan |last5=Green |first5=Emily |last6=Pisani |first6=Davide |last7=Hou |first7=Xianguang |last8=Edgecombe |first8=Gregory D. |last9=Cong |first9=Peiyun |display-authors=6 |date=April 2019 |title=Cambrian sessile, suspension feeding stem-group Ctenophores and evolution of the comb jelly body plan |journal=[[Current Biology]] |lang=en |volume=29 |issue=7 |pages=1112–1125.e2 |doi=10.1016/j.cub.2019.02.036 |doi-access=free |pmid=30905603 |hdl=1983/40a6bcb8-a740-482c-a23c-7d563faea5c5 |hdl-access=free }}</ref><ref>{{Cite journal |last1=Zhao |first1=Yang |last2=Hou |first2=Xian-guang |last3=Cong |first3=Pei-yun |date=January 2023 |title=Tentacular nature of the 'column' of the Cambrian diploblastic ''Xianguangia sinica'' |journal=[[Journal of Systematic Palaeontology]] |lang=en |volume=21 |issue=1 |doi=10.1080/14772019.2023.2215787 |doi-access=free |bibcode=2023JSPal..2115787Z }}</ref>

520&nbsp;million-year-old Cambrian fossils also from Chengjiang in China show a now wholly extinct class of ctenophore, named "[[Scleroctenophora]]", that had a complex internal skeleton with long spines.<ref>{{cite web |last=Mindy |first=Weisberger |date=2015-07-10 |df=dmy-all |title=Ancient jellies had spiny skeletons, no tentacles |website=livescience.com |url=https://www.livescience.com/51515-ancient-comb-jellies-had-skeletons.html |lang=en}}</ref> The skeleton also supported eight soft-bodied flaps, which could have been used for swimming and possibly feeding. One form, ''[[Thaumactena]]'', had a streamlined body resembling that of [[Chaetognatha|arrow worms]] and could have been an agile swimmer.<ref name=Shu-Zhang-etal-2015/>