Editing Nectocaris (section)

==History of study==
<gallery widths="200">
File:USNM PAL 198667 Nectocaris pteryx Image 08.jpg|Holotype of ''Nectocaris'', an incomplete specimen that gave rise to erroneous reconstructions
File:Nectocaris.jpg|Original (and obsolete) reconstruction based on a single, incompletely preserved, lateral specimen (left). The author of this reconstruction, based on the material then available, considered ''Nectocaris'' to bear arthropod and chordate-like features
</gallery>''Nectocaris'' has a long and convoluted history of study. [[Charles Doolittle Walcott]], the discoverer of the Burgess Shale, had photographed the one specimen he had collected in the 1910s, but never had time to investigate it further. As such, it was not until 1976 that ''Nectocaris'' was formally described, by [[Simon Conway Morris]].<ref name=SCM1976>{{cite journal |author=Conway Morris, S. |year=1976 |title=''Nectocaris pteryx'', a new organism from the Middle Cambrian Burgess Shale of British Columbia |volume=12 |pages=703–713 |journal=Neues Jahrbuch für Geologie und Paläontologie, Monatshefte|author-link=Simon Conway Morris }}</ref>

Because the genus was originally known from a single, incomplete specimen and with no [[Counter slab|counterpart]],<ref name="WonderfulLife">{{cite book |author=Gould, S.J. |year=1989 |title=Wonderful Life: The Burgess Shale and the Nature of History |publisher=Hutchison Radius |isbn=978-0-09-174271-3 |bibcode=1989wlbs.book.....G |author-link=Stephen Jay Gould }}</ref> Conway Morris was unable to deduce its affinity. It had some features which were reminiscent of [[arthropod]]s, but these could well have been convergently derived.<ref name=SCM1976/><ref name="Waggoner1996">{{cite journal |last=Waggoner |first=B.M. |year=1996 |title=Phylogenetic hypotheses of the relationships of Arthropods to Precambrian and Cambrian problematic fossil taxa |journal=Systematic Biology |volume=45 |issue=2 |pages=190–222 |jstor=2413615 |doi=10.2307/2413615|doi-access=free }}</ref> Its fins were very unlike those of arthropods.<ref name=SCM1976/>

Working from photographs, the Italian palaeontologist Alberto Simonetta believed he could classify ''Nectocaris'' within the [[chordate]]s.<ref name=Simonetta1988>{{cite journal |author=Simonetta, A.M. |year=1988 |title=Is ''Nectocaris pteryx'' a chordate? |journal=Bollettino di Zoologia |volume=55 |issue=1–2 |pages=63–68 |doi=10.1080/11250008809386601|doi-access=free }}</ref> He focussed mainly on the tail and fin morphology, interpreting Conway Morris's 'gut' as a [[notochord]] – a distinctive chordate feature.<ref name=Simonetta1988/>

The classification of ''Nectocaris'' was revisited in 2010, when Martin Smith and Jean-Bernard Caron described 91&nbsp;additional specimens, many of them better preserved than the type. These allowed them to reinterpret ''Nectocaris'' as a primitive [[cephalopod]], with only 2&nbsp;tentacles instead of the 8 or 10&nbsp;limbs of modern cephalopods. The structure previous researchers had identified as an oval [[carapace]] or shield behind the eyes<ref name=SCM1989>{{cite journal |last=Conway Morris |first=Simon |year=1989 |title=Burgess Shale Faunas and the Cambrian Explosion |journal=Science |volume=246 |issue=4928 |pages=339–346 |bibcode=1989Sci...246..339C |pmid=17747916 |doi=10.1126/science.246.4928.339|s2cid=10491968 }}</ref> was suggested to be a soft funnel, similar to the ones used for propulsion by modern cephalopods. The interpretation would push back the origin of cephalopods by at least 30&nbsp;million years, much closer to the first appearance of complex animals, in the [[Cambrian explosion]], and implied that &ndash; against the widespread expectation &ndash; cephalopods evolved from non-mineralized ancestors.<ref name="SmithAndCaron2010">{{cite journal |last1=Smith |first1=M.R. |last2=Caron |first2=J.B. |year=2010 |title=Primitive soft-bodied cephalopods from the Cambrian |url= https://durham-repository.worktribe.com/output/1430329|journal=Nature |volume=465 |issue=7297 |pages=469–472 |bibcode=2010Natur.465..469S |doi=10.1038/nature09068 |pmid=20505727 |s2cid=4421029 |hdl-access=free |hdl=1807/32368 |df=dmy-all}}</ref>

Later independent analyses questioned the cephalopod interpretation, stating that it did not square with the established theory of [[cephalopod evolution]], and that nectocaridids should be considered ''[[incertae sedis]]'' among [[Bilateria]].<ref name="Mazurek2011">{{cite journal |last1=Mazurek |first1=D. |last2=Zatoń |first2=M. |year=2011 |title=Is ''Nectocaris pteryx'' a cephalopod? |journal=Lethaia |volume=44 |issue=1 |pages=2–4 |doi=10.1111/j.1502-3931.2010.00253.x|bibcode=2011Letha..44....2M }}</ref><ref name="Runnegar2011">{{cite journal |last=Runnegar |first=B. |year=2011 |title=Once again: Is ''Nectocaris pteryx'' a stem-group cephalopod? |journal=Lethaia |volume=44 |issue=4 |page=373 |doi=10.1111/j.1502-3931.2011.00296.x|bibcode=2011Letha..44..373R }}</ref><ref name=":1" /><ref name=":0" />

===''Vetustovermis''===
'''''Vetustovermis''''' (from Latin: "very old worm")<ref name=Glaessner1979>{{cite journal |last=Glaessner |first=M.F. |year=1979 |title=Lower Cambrian Crustacea and annelid worms from Kangaroo Island, South Australia |journal=Alcheringa: An Australasian Journal of Palaeontology |volume=3 |issue=1 |pages=21–29 |doi=10.1080/03115517908565437|bibcode=1979Alch....3...21G }}</ref> is a soft-bodied middle Cambrian [[animal]], known from a single reported fossil specimen from the South Australian [[Emu Bay shale]].  It is probably a junior synonym of ''Nectocaris pteryx''.<ref name="Smith2013c"/>

The original description of ''Vetustovermis'' hedged its bets regarding classification, but tentatively highlighted some similarities with the [[annelid]] worms.<ref name=Glaessner1979/> It was later considered an [[arthropod]],<ref name=Luo1999>{{cite book |author1=Luo, H.-L. |author2=Hu, S.-X. |author3=Chen, L.-Z. |publisher=Yunnan Science & Technology Press |place=Kunming, China |year=1999 |title=Early Cambrian Chengjiang fauna from Kunming region, China}}</ref><ref>{{cite news |url=http://news.bbc.co.uk/2/hi/science/nature/4156544.stm |title=Strange fossil defies grouping |publisher=BBC News}}</ref> and in 2010 Smith and Caron, agreeing that ''[[Petalilium]]'' was at least a close relative of ''Vetustovermis'' (but that treating it as a synonym was premature, given the poor preservation of the ''Vetustovermis'' type), placed it with ''Nectocaris'' in the [[clade]] [[Nectocarididae]].<ref name="SmithAndCaron2010"/>

Early press reports misspelled the genus name as ''Vetusto'''d'''ermis''.

===''Petalilium''===
[[File:Petalilium HK-MF-00001A 098.g2.jpg|thumb|300x300px|Fossil of ''Petalilium'']]
'''''Petalilium''''' (sometimes misspelled '''''Petalium''''')<ref name="Chen2005">{{cite journal |last1=Chen |first1=J.Y. |last2=Huang |first2=D.Y. |last3=Bottjer |first3=D.J. |year=2005 |title=An Early Cambrian problematic fossil: ''Vetustovermis'' and its possible affinities |journal=Proceedings of the Royal Society B |volume=272 |issue=1576 |pages=2003–2007 |pmid=16191609 |doi=10.1098/rspb.2005.3159 |pmc=1559895}}</ref> is an enigmatic genus of [[Cambrian]] organism known from the Haikou area,<ref name=Steiner2005>{{cite journal |last1=Steiner |first1=M. |last2=Zhu |first2=M. |last3=Zhao |first3=Y. |last4=Erdtmann |first4=B. |year=2005 |title=Lower Cambrian Burgess Shale-type fossil associations of South China |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |volume=220 |issue=1–2 |pages=129–152 |bibcode=2005PPP...220..129S |doi=10.1016/j.palaeo.2003.06.001}}</ref> from the Maotianshan mudstone member of the [[Chengjiang biota]].<ref name='Han2006'>{{cite journal |last1=Han |first1=J. |last2=Shu |first2=D. |last3=Zhang |first3=Z. |last4=Liu |first4=J. |last5=Zhang |first5=X. |last6=Yao |first6=Y. |year=2006 |title=Preliminary notes on soft-bodied fossil concentrations from the Early Cambrian Chengjiang deposits |journal=Chinese Science Bulletin |volume=51 |issue=20 |page=2482 |doi=10.1007/s11434-005-2151-0 |bibcode=2006ChSBu..51.2482H|s2cid=129162009 }}</ref> The taxon is a junior synonym of ''Nectocaris pteryx''.<ref name="Smith2013c"/>

Fossils of ''Petalilium''{{efn|''Petalilium'' was originally described as ''Vetustovermis'' by Chen ''et al''. (2005),<ref name="Chen2005"/> but recognised as ''Petalilium'' by Smith & Caron (2010).<ref name="SmithAndCaron2010"/>}} show a [[Anatomical terms of location#Directional terms|dorsoventrally]] flattened body, usually 5 to 6&nbsp;centimetres, but ranging from 1.5 to 10&nbsp;cm. It has an ovate trunk region and a large [[muscle|muscular]] foot, and a head with stalked eyes and a pair of long tentacles. The trunk region possesses about 50&nbsp;soft, flexible, [[Anatomical terms of location#Invertebrate directional terms|transverse]] bars, lateral serialised structures of unknown function. The upper part of the body, interpreted as a [[Mantle (mollusc)|mantle]], is covered with a random array of spines on the back, while gills project underneath. A complete, tubular gut runs the length of the body.

Whilst it was originally described as a [[Phyllocarida|phyllocarid]],<ref name=Luo1999/> and a [[ctenophore]] affinity has been suggested,<ref>{{cite book |author1=Chen, L.Z. |author2=Luo, H.L. |author3=Hu, S.X. |author4=Yin, J.Y. |author5=Jiang, Z.W. |author6=Wu, Z.L. |author7=Li, F. |author8=Chen, A.L. |year=2002 |title=Early Cambrian Chengjiang Fauna in Eastern Yunnan, China |publisher=Yunnan Science and Technology Press |place=Kunming |pages=199 |language=Chinese, English}}</ref> neither interpretation is supported by any compelling evidence.<ref name='Hu2007'>{{cite journal |last1=Hu |first1=S. |last2=Steiner |first2= M. |last3=Zhu |first3=M. |last4=Erdtmann |first4=B.D. |last5=Luo |first5=H. |last6=Chen |first6=L. |last7=Weber |first7=B. |year=2007 |title=Diverse pelagic predators from the Chengjiang Lagerstätte and the establishment of modern-style pelagic ecosystems in the early Cambrian |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |volume=254 |issue=1–2 |pages=307–316 |doi=10.1016/j.palaeo.2007.03.044 |bibcode=2007PPP...254..307H}}</ref>

Some of the characters observed in Chen ''et al''.'s (2005) study<ref name="Chen2005"/> suggested that ''Petalilium'' may be related to ''Nectocaris''.<ref name="SmithAndCaron2010"/>