Editing Nectocaris

{{Short description|Extinct animal genus}}
{{Speciesbox
| genus = Nectocaris
| species = pteryx
| fossil_range = {{Fossil range|Cambrian Stage 3|Wuliuan}}
{{Distinguish| Nectocotis}}
| image = Nectocaris pteryx (ROM 60079).jpg
| image_caption = Specimen ROM 60079
| parent_authority = Conway Morris, 1976
| authority = [[Simon Conway Morris|Conway Morris]], 1976
}}

'''''Nectocaris''''' is a genus of squid-like animal of controversial affinities known from the [[Cambrian]] period. The initial fossils were described from the [[Burgess Shale]] of Canada. Other similar remains possibly referrable to the genus are known from the [[Emu Bay Shale]] of Australia and [[Chengjiang Biota]] of China.

''Nectocaris'' was a free-swimming, predatory or scavenging organism. This lifestyle is reflected in its binomial name: ''Nectocaris'' means "swimming shrimp" (from the [[Ancient Greek]] {{lang|el|νηκτόν}}, ''{{lang|el|[[:wikt:nekton|nekton]]}}'', meaning "swimmer" and {{lang|el|καρίς}}, ''{{lang|el|karis}}'', "shrimp"). Two morphs are known: a small morph, about an inch long, and a large morph, anatomically identical but around four times longer.<ref name="Smith2013c">{{cite journal |last=Smith |first=M.R. |year=2013 |title=Nectocaridid ecology, diversity and affinity: Early origin of a cephalopod-like body plan |journal=Paleobiology |volume=39 |issue=2 |pages=291–321 |doi=10.1666/12029 |bibcode=2013Pbio...39..297S |s2cid=85744624}}</ref>

Nectocaridids have controversial affinities. Some authors have suggested that they represent the earliest known [[Cephalopod|cephalopods]]. However, their morphology is strongly dissimilar to confirmed early cephalopods, and thus their affinities to cephalopods and even to [[Mollusca|molluscs]] more broadly are rejected by most authors.<ref name=":0">{{Cite journal |last1=Pohle |first1=Alexander |last2=Kröger |first2=Björn |last3=Warnock |first3=Rachel C. M. |last4=King |first4=Andy H. |last5=Evans |first5=David H. |last6=Aubrechtová |first6=Martina |last7=Cichowolski |first7=Marcela |last8=Fang |first8=Xiang |last9=Klug |first9=Christian |date=December 2022 |title=Early cephalopod evolution clarified through Bayesian phylogenetic inference |journal=BMC Biology |language=en |volume=20 |issue=1 |pages=88 |doi=10.1186/s12915-022-01284-5 |issn=1741-7007 |pmc=9008929 |pmid=35421982 |doi-access=free }}</ref><ref name=":1" /> Their affinities to any animal group beyond [[Bilateria]] are uncertain, though they have been suggested to be members of [[Lophotrochozoa]].<ref name=":1" />

The closely related Ordovician taxon ''[[Nectocotis]]'' is a second genus, closely resembling ''Nectocaris'', but suggested to have had an internal skeletal element.<ref name=Smith2019>{{cite journal |last=Smith |first=Martin R. |year=2019 |title=An Ordovician nectocaridid hints at an endocochleate origin of Cephalopoda |journal=Journal of Paleontology |pages=64–69 |volume=94 |doi=10.1017/jpa.2019.57 |s2cid=201208912 |url=http://dro.dur.ac.uk/28457/1/28457.pdf}}</ref>

== Anatomy ==
{{Css Image Crop
|Image         = Nectocaris 59660.jpg
|bSize         = 200
|cWidth        = 135
|cHeight       = 270
|oTop          = 15
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|Location      = left
|Description   = ''Nectocaris pteryx'' from the Burgess Shale; funnel is visible folded to left of specimen. Image from Smith (2013).<ref name="Smith2013">{{cite journal | doi=10.1666/12029 | title=Nectocaridid ecology, diversity, and affinity: Early origin of a cephalopod-like body plan | date=2013 | last1=Smith | first1=Martin R. | journal=Paleobiology | volume=39 | issue=2 | pages=297–321 | bibcode=2013Pbio...39..297S | s2cid=85744624 }}</ref>
}}
''Nectocaris'' had a flattened, kite-shaped body with a fleshy fin running along the length of each side.<ref name=SmithAndCaron2010/> The small head had two stalked eyes, a single pair of [[Tentacle|tentacles]], and a flexible funnel-shaped structure opening out to the underside of the body.<ref name=SmithAndCaron2010/> The funnel often gets wider away from the head.<ref name="SmithAndCaron2010" /> The funnel has been suggested to represent an eversible (able to be turned inside out) [[pharynx]].<ref name=":1" /> Internally, a long cavity runs along the body axis, which is suggested to represent the digestive tract.<ref name=":1" /> The body contains a pair of [[gill]]s; the gills comprise blades emerging from a zig-zag axis. Muscle blocks surrounded the axial cavity, and are now preserved as dark blocks in the lateral body.<ref name="Smith2013c"/> The fins also show dark blocks, with fine striations superimposed over them. These striations often stand in high relief above the rock surface itself.<ref name="Smith2013c"/>

== Diversity ==
Although ''Nectocaris'' is known from Canada, China and Australia, in rocks spanning some 20&nbsp;million years, there does not seem to be much diversity; size excepted, all specimens are anatomically very similar.  Historically, three genera have been erected for nectocaridid taxa from different localities, but these 'species' – ''Petalilium latus'' and ''Vetustovermis planus'' – likely belong to the same genus or even the same species as ''N.&nbsp;pteryx''. Within ''N.&nbsp;pteryx'', there seem to be two discrete morphs, one large (~10&nbsp;cm in length), one small (~3&nbsp;cm long). These perhaps represent [[sexual dimorphism|separate male and female forms]].<ref name="Smith2013c"/>

== Ecology ==
[[File:Nectocaris pteryx.jpg|thumb|Life restoration]]
The unusual shape of the nectocaridid funnel has led to its interpretation as an eversible [[proboscis]]. Martin R. Smith and Jean-Bernard Caron have suggested that it was used for [[jet propulsion]],<ref name="SmithAndCaron2010" /><ref name="Smith2013c"/> though this has been questioned by other authors.<ref name="Runnegar2011" /> The eyes of ''Nectocaris'' would have had a similar visual acuity to modern ''[[Nautilus]]'' (if they lacked a lens) or [[squid]] (if they did not).<ref name="Smith2013c"/> They are thought to have been freely-swimming [[nektonic]] organisms,<ref name=":1" /> that were either scavengers or predators on soft-bodied animals, using their tentacles to manipulate food items.<ref name="SmithAndCaron2010" />

== Affinity ==
The affinity of ''Nectocaris'' is controversial.<ref name=Runnegar2011/><ref name=":1" /> Martin R. Smith and Jean-Bernard Caron have suggested that nectocaridids represent early cephalopods. In a 2010 publication in Nature, they suggested that the ancestor of modern cephalopods and nectocaridids probably lacked a mineralised shell,<ref name="SmithAndCaron2010" /> while Smith in a later 2013 publication suggested that it may be more plausible that nectocaridids had instead lost a mineralised shell and developed a morphology convergent on modern [[Coleoidea|coleoids]].<ref name="Smith2013c"/> However, other authors contend that the morphology of nectocaridids is contrary to what is known about cephalopod and mollusc evolution, and they cannot be accommodated within these groups,<ref name=":0" /><ref name=":1" /><ref name="Runnegar2011" /> and can only be confidently placed as members of [[Bilateria]].<ref name=":1">{{Cite journal |last1=Kröger |first1=Björn |last2=Vinther |first2=Jakob |last3=Fuchs |first3=Dirk |date=August 2011 |title=Cephalopod origin and evolution: A congruent picture emerging from fossils, development and molecules |url=https://onlinelibrary.wiley.com/doi/10.1002/bies.201100001 |journal=BioEssays |language=en |volume=33 |issue=8 |pages=602–613 |doi=10.1002/bies.201100001|pmid=21681989 |s2cid=2767810 |url-access=subscription }}</ref>

==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"/>

==See also==
{{Portal|paleontology}}
* [[Cambrian explosion]]
* [[Paleobiota of the Burgess Shale]]
* [[Chengjiang biota]]
** [[List of Chengjiang Biota species by phylum]]

== Footnotes ==
{{notelist|1}}

==References==
{{reflist|25em}}

==Further reading==
* {{Cite web|date=2011|title=''Nectocaris pteryx''|work=Burgess Shale Fossil Gallery|publisher=Virtual Museum of Canada|url=http://burgess-shale.rom.on.ca/en/fossil-gallery/view-species.php?id=87|archive-url=https://web.archive.org/20201112025257/http://burgess-shale.rom.on.ca/en/fossil-gallery/view-species.php?id=87|archive-date=2020-11-12|url-status=dead}} – 3D animations are available and a more detailed consideration of ''Nectocaris''

* {{cite magazine |author=Switek, Brian |date=5 July 2011 |title=Nectocaris: What the heck is this thing? |magazine=Laelaps |url=https://www.wired.com/wiredscience/2011/07/nectocaris-what-the-heck-is-this-thing/}} – Brian Switek discusses the taxonomy and history of ''Nectocaris'' in his blog 

* {{cite news |author=Moskvitch, Katia |date=27 May 2010 |url=http://news.bbc.co.uk/1/hi/science_and_environment/10173293.stm |title=Mystery fossil is ancestor of squid |publisher=[[BBC News]]}} – [[BBC News]] coverage of the Smith & Caron's (2010) re-description

* {{cite web |author=Taylor, Christopher |date=14 January 2011 |title=So nice when people agree with you |work=Catalogue of Organisms |url=http://coo.fieldofscience.com/2011/01/so-nice-when-people-agree-with-you.html}} – a blog article supporting Mazurek & Zatoń's (2011) view

*{{Crucibleofcreation}}

==External links==
*{{commons category-inline|Nectocaris|''Nectocaris''}}

{{Taxonbar|from=Q132992}}

[[Category:Nectocarididae]]
[[Category:Burgess Shale animals]]
[[Category:Cambrian Series 2 first appearances]]
[[Category:Miaolingian extinctions]]
[[Category:Maotianshan shales fossils]]
[[Category:Prehistoric cephalopod genera]]
[[Category:Prehistoric invertebrates of Oceania]]
[[Category:Controversial taxa]]
[[Category:Fossil taxa described in 1976]]
[[Category:Emu Bay Shale]]
[[Category:Cambrian genus extinctions]]