Marrellomorpha

{{Short description|Extinct class of arthropods}} {{Automatic taxobox | name = Marrellomorpha | fossil_range = Middle Cambrian - Early Devonian, {{fossilrange|508|390}} | image = Marrella.png | image_caption = Life restoration of ''Marrella'' (Marrellida) | image2 = Primicaris larvaformis diagrammatic reconstruction.svg | image2_caption = Diagram of ''Primicaris'' (Acercostraca) | taxon = Marrellomorpha | authority = Beurlen, 1930 | subdivision_ranks = Subgroups | subdivision_ref = | subdivision = *'''Acercostraca''' **''Primicaris'' **''Skania'' **Vachonisiidae *** ''Xylokorys'' *** ''Vachonisia'' *** ''Enosiaspis'' *'''Marrellida''' **''Marrella'' ** ''Furca'' ** ''Mimetaster'' ** ''Tomlinsonus'' }}

'''Marrellomorpha''' are an extinct group of arthropods known from the Cambrian to the Early Devonian.<ref name="app"/> It is divided into two major groups, '''Marrellida''' and '''Acercostraca'''. They lacked mineralised hard parts, so are only known from areas of exceptional preservation, limiting their fossil distribution. The best known member is ''Marrella'', with thousands of specimens found in the Cambrian aged Burgess Shale of Canada.

==Description and ecology== The group is divided up into two major orders, Marrellida and Acercostraca. Both groups have cuticles (exoskeletons) that are not mineralised, unbranched antennae attached to the head section (cephalon) and a segmented trunk (reaching over 25 segments in adult individuals in some species<ref name=":3" />) with a pair of biramous (divided into two branches) appendages attached to each trunk segment except the last. Marrellida is recognised by the possession of head shields with two or three pairs of elongate spine-like projections, and two or three attached pairs of uniramous (single-branched) head appendages (including the antennae), while Acercostraca have large ovoid dorsal shields that cover the entire upper half of the body, and up to five pairs of appendages attached to the head section.<ref name=":0" />

The trunks of marrellids are divided into numerous cylindrically-shaped segments. The endopods (lower, leg-like branches) of the biramous trunk limbs of marrellids have six segments (podomeres). The exopods (outer/upper branches of the two-branched biramous trunk limbs) of marrellids had an annulated appearance, and had numerous attached elongate lammelate setae (hair-like structures) and are thought to have functioned for respiration.<ref name=":2">{{Cite journal |last1=Laibl |first1=Lukáš |last2=Gueriau |first2=Pierre |last3=Saleh |first3=Farid |last4=Pérez-Peris |first4=Francesc |last5=Lustri |first5=Lorenzo |last6=Drage |first6=Harriet B. |last7=Bath Enright |first7=Orla G. |last8=Potin |first8=Gaëtan J.-M. |last9=Daley |first9=Allison C. |date=2023-09-25 |title=Early developmental stages of a Lower Ordovician marrellid from Morocco suggest simple ontogenetic niche differentiation in early euarthropods |journal=Frontiers in Ecology and Evolution |volume=11 |bibcode=2023FrEEv..1132612L |doi=10.3389/fevo.2023.1232612 |issn=2296-701X |doi-access=free |article-number=1232612}}</ref> The trunk limb exopods of at least some acercostracans were similar to those of marrellids.<ref name=":3" />

Marrellids are either suggested to have swum close to the seafloor (''Marrella'') or have lived walking along the sea floor (other marrellids) and to have used their hind trunk appendages to sift food particles, which were then passed forward by the limbs to the mouth.<ref name=":2" /> The posterior trunk appendages of at least some vachonisiid acercostracans have been suggested to have been used the same way, and are also suggested to have lived on the seafloor.<ref name=":2" /><ref>{{Cite journal |last=Siveter |first=Derek J |last2=Fortey |first2=Richard A |last3=Sutton |first3=Mark D |last4=Briggs |first4=Derek E.G |last5=Siveter |first5=David J |date=2007-09-22 |title=A Silurian ‘marrellomorph’ arthropod |url=https://royalsocietypublishing.org/doi/10.1098/rspb.2007.0712 |journal=Proceedings of the Royal Society B: Biological Sciences |language=en |volume=274 |issue=1623 |pages=2223–2229 |doi=10.1098/rspb.2007.0712 |issn=0962-8452 |pmc=2287322 |pmid=17646139}}</ref>

== Taxonomy == === Internal taxonomy=== Internal taxonomy of Marrellomorpha after Moysiuk ''et al.'', 2022.<ref name=":0">{{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/product/identifier/S0022336022000117/type/journal_article |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|doi-access=free }}</ref> * Acercostraca Lehmann, 1955 ** ''Skania<ref name=":3">{{Cite journal |last=Legg |first=D.A. |date=2015-09-30 |title=The morphology and affinities of ''Skania fragilis'' (Arthropoda) from the middle Cambrian Burgess Shale |url=http://www.geology.cz/bulletin/contents/art1532 |journal=Bulletin of Geosciences |language=en |pages=509–518 |doi=10.3140/bull.geosci.1532 |issn=1802-8225 |doi-access=free}}</ref>'' Burgess Shale, Canada, Cambrian (Miaolingian) ? Kaili Formation, China, Cambrian (Wuliuan) ** ''Primicaris'' Burgess Shale, Canada, Cambrian (Miaolingian), Maotianshan Shales, China, Cambrian Stage 3 ** Vachonisiidae Tasch, 1969 *** ''Xylokorys'' Coalbrookdale Formation, England, Silurian (Wenlock) *** ''Vachonisia'' Hunsrück Slate, Germany, Lower Devonian (Emsian) *** ''Enosiaspis'' Fezouata Formation, Morocco, Early Ordovician (Floian) * Marrellida Størmer, 1959, pro Marrellina Raymond, 1920 ** ''Marrella'' Balang Formation, China, Cambrian Stage 4 Kaili Formation, China, Cambrian (Wuliuan), Burgess Shale, Canada, Cambrian (Miaolingian) ** ''Furca'' Letná Formation'','' Czech Republic, Upper Ordovician (Sandbian) ** "Furca mauretanica" (''nomen nudum'') Fezouata Formation, Morocco, Early Ordovician (Floian) ** ''"Mimetaster" florestaensis'' Floresta Formation Argentina, Lower Ordovician (Tremadocian) ** Mimetasteridae Birenheide, 1971 *** ''Tomlinsonus'' Kirkfield Formation, Canada, Late Ordovician (Katian) *** ''Mimetaster'' Hunsrück Slate, Germany, Lower Devonian (Emsian)

Fragmentary taxa assigned to Marrellomorpha include ''Austromarrella'' from Cambrian Series 3 aged deposits in Australia,<ref>{{Cite journal |last1=Haug|first1=Joachim T. | last2=Castellani|first2=Christopher | last3=Haug|first3=Carolin | last4=Waloszek|first4=Dieter | last5=Maas|first5=Andreas | date=2012 |title=A ''Marrella''-like arthropod from the Cambrian of Australia: A new link between "Orsten"-type and Burgess Shale assemblages|url=http://www.app.pan.pl/article/item/app20110120.html |journal=Acta Palaeontologica Polonica |volume=58 | issue=3 | pages=629–639 |doi=10.4202/app.2011.0120|doi-access=free }}</ref> and ''Dyrnwynia'' from the Ordovician (Darriwilian) aged Llanfallteg Formation of Wales, which in its original description was assigned to Marrellida.<ref>{{Cite journal |last=Legg |first=David |date=2016 |title=A new marrellid arthropod from the Ordovician of Wales |journal=Acta Palaeontologica Polonica |volume=61 |doi=10.4202/app.00246.2016 |issn=0567-7920|doi-access=free }}</ref>

Some studies have recovered Marrellomorpha as paraphyletic, with Marrellida and Acercostraca more closely related to other arthropods than they are to each other.<ref name=":1" />

==== Gallery ==== {{gallery|File:Xylokorys chledophilia.png|Ventral reconstruction of ''Xylokorys''|File:Furca bohemica reconstruction.png|Reconstruction of the head shield of ''Furca bohemica''|File:Furca mauritanica MHNT.jpg|Fossil of "Furca mauretanica"|File:Mimetaster hexagonalis reconstruction.jpg|Reconstruction of ''Mimetaster''|File:Vachonisia rogeri.png|Restoration of ''Vachonisia''|Tomlinsonus.png|Life restoration of ''Tomlinsonus''|width=200|height=180|File:Primicaris.png|Life restoration of ''Primicaris''|Skania diagram.png|Diagram of ''Skania''}}

===Relationship to other arthropods=== Their phylogenetic position within arthropoda is uncertain, beyond being placed in Deuteropoda for their possession of biramous appendages. Various studies have alternatively placed them in the Arachnomorpha as relatives of Artiopoda (trilobites and kin), as related to Mandibulata (the group containing crustaceans, insects and myriapods), or as stem group euarthropods.<ref name=":0" /> The engimatic Cambrian arthropod ''Burgessia'' may be closely related to marrellomorphs.<ref>{{Cite journal |last1=Ortega-Hernández |first1=Javier |last2=Legg |first2=David A. |last3=Braddy |first3=Simon J. |date=February 2013 |title=The phylogeny of aglaspidid arthropods and the internal relationships within Artiopoda |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1096-0031.2012.00413.x |journal=Cladistics |language=en |volume=29 |issue=1 |pages=15–45 |doi=10.1111/j.1096-0031.2012.00413.x |pmid=34814371 |issn=0748-3007|url-access=subscription }}</ref> Some authors have proposed that they may be closely related to sea spiders (Pycnogonida) within Chelicerata though the cladistical support for such a relationship is relatively weak.<ref name=":0" /> A 2025 paper found Marrellomorpha to be within total-group Mandibulata, as a paraphyletic group at the base of Artiopoda.<ref name=":1">{{cite journal |last1=Liu |first1=Yao |last2=Zeng |first2=Han |last3=Zhao |first3=Fangchen |last4=Zhu |first4=Yuyan |last5=Li |first5=Yimeng |last6=Yin |first6=Zongjun |last7=Zhu |first7=Maoyan |title=A tiny Cambrian stem-mandibulate reveals independent evolution of limb tagmatization and specialization in early euarthropods |journal=Scientific Reports |date=31 May 2025 |volume=15 |issue=1 |doi=10.1038/s41598-025-03544-0|pmc=12126567 }}</ref> ===Phylogeny=== ====Internal phylogeny==== After Legg, 2016.<ref>{{Cite journal |last=Legg |first=David A. |date=2016-02-27 |title=An acercostracan marrellomorph (Euarthropoda) from the Lower Ordovician of Morocco |url=https://doi.org/10.1007/s00114-016-1352-5 |journal=The Science of Nature |language=en |volume=103 |issue=3 |pages=21 |doi=10.1007/s00114-016-1352-5 |pmid=26922777 |bibcode=2016SciNa.103...21L |issn=1432-1904|url-access=subscription }}</ref> {{clade |{{clade |1 = Outgroups |label2 = Marrellomorpha |2 = {{clade |label1 = Marrellida |1 = {{clade |1 = ''Marrella splendens'' 70px |label2 = Mimetasteridae |2 = {{clade |1 = ''Furca bohemica'' 60px |2 = {{clade |1 = Moroccan marrellid ("Furca mauretanica") 70px |2 = ''Mimetaster hexagonalis'' 80px }} }} }} |label2 = Acercostraca |2 = {{clade |1 = ''Skania fragilis'' 100px |2 = {{clade |1 = ''Primicaris larvaformis'' 70px |2 = {{clade |1 = "''Skania''" ''sundbergi'' 60px |label2 = Vachonisiidae |2 = {{clade |1 = ''Enosiaspis hrungnir'' 60px |2 = {{clade |1 = ''Xylokorys chledophilia'' 60px |2 = ''Vachonisia rogeri'' 60px }} }} }} }} }} }} }} }} After Moysiuk ''et al.'', 2022.<ref name=":0"/> {{barlabel |size=10 |at1=4.8|label1=Taxa usually not considered marrellomorphs |cladogram= {{clade |{{clade |1 = {{clade |1 = {{clade |label1=Marrellomorpha |1 = {{clade |1 = {{clade |label1 = Marrellida |1 = {{clade |1 = {{clade |1 = {{clade |1 = "''Mimetaster''" ''florestaensis'' 60px |2 = ''Furca bohemica'' 60px }} |2 = {{clade |1 = ''Mimetaster hexagonalis'' 80px |2 = ''Tomlinsonus dimitrii'' 80px }} |3 = Moroccan marrellid ("Furca mauretanica") 70px }} |2 = ''Marrella'' 70px }} |2 = {{clade |1 = {{clade |1 = ''Palaeoisopus'' 80px|bar1=purple |2 = ''Haliestes'' 70px|bar2=purple }} |2 = ''Aquilonifer'' 90px|bar2=purple }} }} |label2=Acercostraca |2 = {{clade |1 = {{clade |1 = {{clade |1 = ''Vachonisia'' 60px |2 = ''Xylokorys'' 60px }} |2 = ''Enosiaspis'' 60px }} |2 = {{clade |1 = ''Skania'' 100px |2 = ''Primicaris'' 70px }} }} }} |2 = ''Eoredlichia'' |3 = ''Mollisonia'' 80px }} |2 = {{clade |1 = ''Waptia'' 90px |2 = ''Tokummia'' 80px }} }} |2 = ''Kylinxia'' 80px }} }} }}

====External phylogeny==== Implied weights maximum parsimony phylogeny of Arthropoda after Liu et al. 2025, which recovered "Marrellomorpha" as a paraphyletic group at the base of Artiopoda (the group which includes trilobites and their relatives), related to Mandibulata.<ref name=":1" />{{clade |label1=Arthropoda |1={{clade |1=†Radiodonta (e.g. ''Anomalocaris'') 100px |label2=Deuteropoda |2={{clade |1={{clade |1=†Megacheira 100px |2=Pan-Chelicerata (sea spiders, horseshoe crabs, arachnids, etc) 100px }}

|2={{clade |1={{clade |1=†"Great appendage bivalved forms" 100px |2=†Isoxyida 100px }} |2={{clade |1={{clade |1=†'''Marrellida''' 100px |2={{clade |1=†'''Acercostraca''' 100px |2=†Artiopoda (including Trilobita)100px }} }} |label2=Mandibulata |2={{clade |1={{clade |1=†Fuxianhuiida 100px |2=Myriapoda (millipedes, centipedes, etc) 100px }} |2={{clade |1=Pancrustacea (crustaceans, insects, etc) |2=†Hymenocarina 100px}} }}}}}}}}}}}}

==References== <references> <ref name="app">{{Cite journal | title = A revision of the Late Ordovician marrellomorph arthropod ''Furca bohemica'' from Czech Republic| journal = Acta Palaeontologica Polonica | volume = 58 | issue = 3 | pages = 615–628 | year = 2012| last1 = Rak | first1 = Štĕpán| last2=Ortega-Hernández|first2=Javier | last3=Legg|first3=David A. | doi = 10.4202/app.2011.0038| doi-access = free}}</ref> </references>

Category:Marrellomorpha Category:Paleozoic arthropods Category:Arthropod classes