Editing Marrella

{{Short description|Extinct genus of Arthropods}}
{{Other uses|Marella (disambiguation)}}
{{Italic title}}
{{Speciesbox
| fossil_range = {{fossil range|Mid Cambrian|latest=Early Ordovician}}
| image = USNM PAL 57674 Marrella splendens Image 01.jpg
| image_caption = Fossil [[Type_(biology)#Lectotype|lectotype]] of ''Marrella'', USNM PAL 57674
| image2 = Marrella.png
| image2_caption = Life reconstruction of ''Marrella''
| genus = Marrella
| parent_authority = Walcott, 1912
| species = splendens
| authority = [[Charles Doolittle Walcott|Walcott]], 1912
}}

'''''Marrella''''' is an extinct [[genus]] of [[marrellomorph]] [[arthropod]] known from the [[Middle Cambrian]] of North America and Asia. It is the most common animal represented in the [[Burgess Shale]] of British Columbia, Canada, with tens of thousands of specimens collected. Much rarer remains are also known from deposits in China.

==History==
''Marrella'' was the first fossil collected by [[Charles Doolittle Walcott]] from the Burgess Shale, in 1909.<ref>{{cite book|last= Gould|first= Stephen Jay|author-link= Stephen Jay Gould|title= Wonderful Life: Burgess Shale and the Nature of History|publisher= [[Vintage Books|Vintage]]|year= 2000|page=108|isbn= 978-0-09-927345-5|oclc= 45316756|url=https://books.google.com/books?id=SjpSkzjIzfsC&pg=PA108}} Also {{OCLC|44058853}}.</ref> Walcott described ''Marrella'' informally as a "lace crab" and described it more formally as an odd [[Trilobita|trilobite]]. It was later reassigned to the now defunct [[class (biology)|class]] Trilobitoidea in the ''[[Treatise on Invertebrate Paleontology]]''. In 1971, [[Harry B. Whittington|Whittington]] undertook a thorough redescription of the animal and, on the basis of its legs, [[gill]]s and head appendages, concluded that it was neither a trilobite, nor a [[Chelicerata|chelicerate]], nor a [[crustacean]].<ref name="Whittington1971">{{cite journal |last=Whittington |first=H. B. |year=1971 |title=Redescription of Marrella splendens (Trilobitoidea) from the Burgess Shale, Middle Cambrian, British Columbia |url=https://ftp.maps.canada.ca/pub/nrcan_rncan/publications/STPublications_PublicationsST/102/102427/bu_209.pdf |journal=Bulletin – Geological Survey of Canada |publisher=[[Geological Survey of Canada]] |volume=209 |pages=1–24}}</ref>

''Marrella'' is one of several unique arthropod-like organisms found in the Burgess Shale. Other examples are ''[[Opabinia]]'' and ''[[Yohoia]]''. The unusual and varied characteristics of these creatures were startling at the time of discovery. The fossils, when described, helped to demonstrate that the soft-bodied Burgess fauna was more complex and diverse than had previously been anticipated.<ref>{{cite book|last= Gould|first= Stephen Jay|author-link= Stephen Jay Gould|title= Wonderful Life: Burgess Shale and the Nature of History|publisher= [[Vintage Books|Vintage]]|year= 2000|page=173|isbn= 978-0-09-927345-5|oclc= 45316756|url=https://books.google.com/books?id=SjpSkzjIzfsC&pg=PA173}} Also {{OCLC|44058853}}.</ref>

==Morphology==
[[File:Marrella splendens by Haug et al.png|thumb|350px|''Marrella splendens'' by Haug et al. [[2012 in paleontology|2012]]<ref>Haug, J. T., Castellani, C., Haug, C., Waloszek, D., Maas, A. (2012). A Marrella−like arthropod from the Cambrian of Australia: a new link between "Orsten"−type and Burgess Shale assemblages. Acta Palaeontologica Polonica 58: 629–639. doi:10.4202/app.2011.0120</ref><br />Top left– dorsal view on a rendered 3D model<br />
top right and centre right– micrographs under polarized light
<br />
top right – well preserved specimen USNM 83486f with the exopods in a "rusty" preservation (cf. García−Bellido and Collins 2006)
<br />
bottom left – stereo image of specimen USNM 139665. Exopods of preceding limbs are super−imposing each other, separated by a thin layer of sediment
<br />
bottom right – detail of specimen ROM 56766A in "rusty" preservation. Here the spines on the lateral side of the exopod ringlets are well preserved
<br />
centre right – one of the smallest specimens of ''M. splendens'' USNM 219817e that possesses preserved appendage remains Black bars for centre right image = 0.6mm, rest = 1mm|left]]
Specimens of ''Marrella'' range from {{Convert|2.4 to 24.5|mm|in|abbr=|frac=32}} in length. The head shield had two pairs of long posteriorly curved projections/spines, the posterior pair of which had a serrated keel. There is no evidence of eyes. On the underside of the head was a pair of long and sweeping flexible [[antenna (biology)|antennae]], composed of about total 30 segments, projecting forward at an angle of 15 to 30 degrees away from the midline. On part of the antennae, the joints between segments bear [[seta]]e. Behind and slightly above the antennae attached a pair of short and stout paddle-like swimming appendages, composed of one long basal segment and five shorter segments, the edges of the latter of which were fringed with [[seta]]e (hair-like structures).<ref name=":0" /><ref name="Whittington1971" />

The body had a minimum of 17 segments ([[Tagma (biology)|tagma]]), increasing to over 26 segments in larger specimens, each with a pair of [[biramous]] (two-branched) appendages. The lower branches of each appendage (the [[endopod]]) were elongate and leg-like with 5 segments/podomeres excluding the basal segment/basipod, with the terminal segments being tipped with claws. The endopods sequentially decreased in size posteriorly, with the size reduction accelerating beyond the 9th pair. The upper branch (the [[exopod]]), which functioned as gill was segmented and bore thin filamentous structures. There is a tiny, button-like [[telson]] at the end of the [[Thorax (arthropod anatomy)|thorax]].<ref name=":0">García-Bellido, Diego & Collins, Desmond. (2006). A new study of Marrella splendens (Arthropoda, Marrellomorpha) from the Middle Cambrian Burgess Shale, British Columbia, Canada. Canadian Journal of Earth Sciences. 43. 721-742. 10.1139/e06-012.</ref><ref name="Whittington1971" />

A 1998 paper suggested that striations present on the front projection of well-preserved specimens of ''Marrella'' represented a [[diffraction grating]] pattern, that in life would have resulted in an [[iridescent]] sheen.<ref name="Parker1998">{{cite journal |last= Parker|first= A. R.|year= 1998|title= Colour in Burgess Shale animals and the effect of light on evolution in the Cambrian|journal= Proceedings of the Royal Society B: Biological Sciences|volume= 265|issue= 1400|pages= 967–972|doi=10.1098/rspb.1998.0385|pmc= 1689164}}</ref> However the conclusions of the paper regarding other animals with supposed iridescent diffraction gratings have been questioned by other authors.<ref>{{Cite journal |last=Smith |first=Martin R. |date=January 2014 |editor-last=Lane |editor-first=Phil |title=Ontogeny, morphology and taxonomy of the soft-bodied Cambrian 'mollusc' Wiwaxia |journal=Palaeontology |language=en |volume=57 |issue=1 |pages=215–229 |doi=10.1111/pala.12063 |bibcode=2014Palgy..57..215S |s2cid=84616434 |quote=The full width of each sclerite [of ''Wiwaxia''] is striated by finely spaced longitudinal lineations. Parker (1998) argued that these were superficial – although they are not visible on surfaces imaged under SEM and do not exhibit interference under transmitted light, so might be better interpreted as internal channels indicating microvillar secretion.|doi-access=free }}</ref><ref>{{Cite journal |last1=Parry |first1=Luke |last2=Caron |first2=Jean-Bernard |date=2019-09-06 |title=Canadia spinosa and the early evolution of the annelid nervous system |journal=Science Advances |language=en |volume=5 |issue=9 |pages=eaax5858 |doi=10.1126/sciadv.aax5858 |issn=2375-2548 |pmc=6739095 |pmid=31535028 |bibcode=2019SciA....5.5858P |quote=In Canadia, longitudinal striations along chaetae, which have previously interpreted as external evidence for iridescence, are concordant with the dimensions of microvilli and represent internal rather than external features.}}</ref> Dark stains are often present at the posterior regions of specimens, probably representing extruded waste matter<ref name="Whittington1978">{{Cite journal | last1 = Whittington | first1 = H. B. | title = The Lobopod Animal ''Aysheaia pedunculata'' Walcott, Middle Cambrian, Burgess Shale, British Columbia | pages = 165–197 | journal = Phil. Trans. R. Soc. Lond. B | volume = 284| issue = 1000| doi =  10.1098/rstb.1978.0061| year = 1978 |bibcode = 1978RSPTB.284..165W | doi-access = free }}</ref> or [[hemolymph]].<ref>{{cite conference| url =http://gsa.confex.com/gsa/2010RM/finalprogram/abstract_171740.htm| title = Synchrotron Imaging of Burgess Shale Fossils: Evidence for Biochemical Copper (Hemocyanin) in the Middle Cambrian Arthropod ''Marrella splendens'' | last1 = Pratt |first1 = Brian R.| last2 = Pushie | first2 = M. Jake | last3 = Pickering | first3 = Ingrid J.| last4 = George | first4 = Graham N. | archive-url = https://web.archive.org/web/20160309172618/http://gsa.confex.com/gsa/2010RM/finalprogram/abstract_171740.htm | archive-date = 2016-03-09 }}</ref> A single specimen caught in the act of [[ecdysis]] ([[moulting]]) is known, which shows that the exoskeleton split at the front of the shield.<ref>{{Cite journal |last1=Drage |first1=Harriet B. |last2=Legg |first2=David A. |last3=Daley |first3=Allison C. |date=2023-08-21 |title=Novel marrellomorph moulting behaviour preserved in the Lower Ordovician Fezouata Shale, Morocco |journal=Frontiers in Ecology and Evolution |volume=11 |doi=10.3389/fevo.2023.1226924 |issn=2296-701X|doi-access=free }}</ref><ref>{{Cite journal |last1=García-Bellido |first1=Diego C. |last2=Collins |first2=Desmond H. |date=May 2004 |title=Moulting arthropod caught in the act |journal=Nature |language=en |volume=429 |issue=6987 |pages=40 |doi=10.1038/429040a |issn=0028-0836|doi-access=free |pmid=15129272 |bibcode=2004Natur.429...40G }}</ref>

==Ecology==
''Marrella'' is likely to have been an active swimmer that swam close to the seafloor (nektobenthic) with its swimming appendages used in a [[backstroke]] motion, with the large spines acting as stabilizers, as well as possibly also having a defensive function. They have been suggested to be [[filter feeder]]s, with food particles sifted out of the water column by the posterior appendages during swimming before being passed forward by the appendages towards the mouth.<ref name=":0" />

==Taxonomy==
''Marrella'' is placed within the [[Marrellida]] clade of the [[Marrellomorpha]], a group of arthropods with uncertain affinities known from the [[Cambrian]] to [[Devonian]]. Within the Marrellida, is it placed as the most [[Basal (phylogenetics)|basal]] known member of the group. Cladogram of Marrellida after Moysiuk et al. 2022<ref>{{Cite journal |last1=Moysiuk |first1=Joseph |last2=Izquierdo-López |first2=Alejandro |last3=Kampouris |first3=George E. |last4=Caron |first4=Jean-Bernard |date=July 2022 |title=A new marrellomorph arthropod from southern Ontario: a rare case of soft-tissue preservation on a Late Ordovician open marine shelf |url=https://www.cambridge.org/core/journals/journal-of-paleontology/article/abs/new-marrellomorph-arthropod-from-southern-ontario-a-rare-case-of-softtissue-preservation-on-a-late-ordovician-open-marine-shelf/2842CB067540110E7212E88AE26BA1B0 |journal=Journal of Paleontology |language=en |volume=96 |issue=4 |pages=859–874 |doi=10.1017/jpa.2022.11 |bibcode=2022JPal...96..859M |issn=0022-3360}}</ref> {{clade
|label1 = Marrellida
|1 = {{clade
|1 = {{clade
|1 = {{clade
|1 = [[Mimetaster#"''Mimetaster''" ''florestaensis''|"''Mimetaster''" ''florestaensis'']] [[File:Mimetaster florestaensis carapace.png|60px]]
|2 = ''[[Furca (genus)|Furca bohemica]]'' [[File:Furca bohemica reconstruction.png|60px]]
}}
|2 = {{clade
|1 = ''[[Mimetaster|Mimetaster hexagonalis]]'' [[File:Mimetaster hexagonalis reconstruction.jpg|80px]]
|2 = ''[[Tomlinsonus|Tomlinsonus dimitrii]]'' [[File:Tomlinsonus (white background).png|80px]]
}}
|3 = Moroccan marrellid [[File:Furca mauritanica diagram.png|70px]]
}}
|2 = '''''Marrella''''' [[File:Marrella.png|70px]]
}}|align=right}}

==Occurrence==
Marrella is the most abundant genus in the [[Burgess Shale]].<ref name="Bottjer">{{cite book |author1=Bottjer, David J. |author2=Etter, Walter |author3=Hagadorn, James W. |author4=Tang, Carol M. |title=Exceptional Fossil Preservation: A unique view on the evolution of marine life |publisher=[[Columbia University Press]] |year=2002 |page=70 |isbn=978-0-231-10255-1 |oclc=47650949}}</ref> Most ''Marrella'' specimens herald from the 'Marrella bed', a thin horizon, but it is common in most other outcrops of the shale. Over 25,000&nbsp;specimens have been collected.<ref name="moulting">{{cite journal |last1=García-Bellido |first1=D. C. |last2=Collins |first2=D. H. |year=2004 |title=Moulting arthropod caught in the act |journal=[[Nature (journal)|Nature]] |volume=429 |issue=6987 |pages=40 |bibcode=2004Natur.429...40G |doi=10.1038/429040a |pmid=15129272 |s2cid=40015864|doi-access=free }}</ref> 5028 specimens of ''Marrella'' are known from the Greater [[Phyllopod bed]], where they comprise 9.56% of the community.<ref name=Caron2006>{{cite journal|last1=Caron |first1=Jean-Bernard|last2=Jackson |first2=Donald A.|title=Taphonomy of the Greater Phyllopod Bed community, Burgess Shale|journal=PALAIOS |volume=21 |issue=5 |pages=451–65|date=October 2006|doi=10.2110/palo.2003.P05-070R|jstor=20173022|bibcode=2006Palai..21..451C |s2cid=53646959 }}</ref>

A few dozen specimens of an indeterminate species of ''Marrella'' have been reported from the [[Kaili Formation]] of Yunnan, China, dating to the [[Wuliuan]] stage of the Cambrian. A single fragmentary specimen of an indeterminate species is also known from the [[Balang Formation]] of Yunnan, China, dating to [[Cambrian Stage 4]]. Both deposits are earlier than the Burgess Shale.<ref>{{Cite journal |last=Liu |first=Qing |date=May 2013 |title=The First Discovery of ''Marrella'' (Arthropoda, Marrellomorpha) from the Balang Formation (Cambrian Series 2) in Hunan, China |url=http://dx.doi.org/10.1666/12-118.1 |journal=Journal of Paleontology |volume=87 |issue=3 |pages=391–394 |doi=10.1666/12-118.1 |bibcode=2013JPal...87..391L |s2cid=129018525 |issn=0022-3360|url-access=subscription }}</ref>{{Clear}}

== See also ==
* [[Paleobiota of the Burgess Shale]]

==References==
{{Reflist}}

==External links==
{{Commons category}}
* {{Cite web|date=2011|title=''Marrella splendens''|work=Burgess Shale Fossil Gallery|publisher=Virtual Museum of Canada|url=http://burgess-shale.rom.on.ca/en/fossil-gallery/view-species.php?id=80|archive-url=https://web.archive.org/20201112025257/http://burgess-shale.rom.on.ca/en/fossil-gallery/view-species.php?id=80|archive-date=2020-11-12|url-status=dead}}
*{{cite web |url=http://paleobiology.si.edu/PaleoArt/Historical/Highlights/marella.html |title=Reconstruction of ''Marrella'' from the collections of Charles Doolittle Walcott |publisher=[[National Museum of Natural History]] |work=Historical Art Gallery}}

{{Taxonbar|from=Q12015622}}

[[Category:Marrellomorpha]]
[[Category:Burgess Shale fossils]]
[[Category:Cambrian arthropods of North America]]
[[Category:Cambrian genus extinctions]]