Marrellomorpha are an extinct group of

arthropod Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and Arth ...

s known from the

Cambrian The Cambrian Period ( ; sometimes symbolized Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million years ag ...

to the

Early Devonian The Early Devonian is the first of three epochs comprising the Devonian period, corresponding to the Lower Devonian series. It lasted from and began with the Lochkovian Stage , which was followed by the Pragian from and then by the Emsian, whi ...

. They lacked mineralised hard parts, so are only known from areas of exceptional preservation, limiting their fossil distribution. The best known member is ''

Marrella ''Marrella'' is an extinct genus of marrellomorph arthropod known from the middle Cambrian Burgess Shale of British Columbia. It is the most common animal represented in the Burgess Shale, with tens of thousands of specimens collected. Much rar ...

'', with thousands of specimens found in the Cambrian aged

Burgess Shale The Burgess Shale is a fossil-bearing deposit exposed in the Canadian Rockies of British Columbia, Canada. It is famous for the exceptional preservation of the soft parts of its fossils. At old (middle Cambrian), it is one of the earliest fos ...

of Canada. The group is divided up into two major orders, Marrellida and Acercostraca. Marrellida is recognised by the possession of head shields with two or three pairs of elongate spine-like projections, and three pairs of

uniramous The arthropod leg is a form of jointed appendage of arthropods, usually used for walking. Many of the terms used for arthropod leg segments (called podomeres) are of Latin origin, and may be confused with terms for bones: ''coxa'' (meaning hip, plur ...

appendages on the

cephalon Cephalon, Inc. was an American biopharmaceutical company co-founded in 1987 by pharmacologist Frank Baldino, Jr., neuroscientist Michael Lewis, and organic chemist James C. Kauer—all three former scientists with the DuPont Company. Baldino ...

, while Acercostraca generally have large ovoid

carapaces A carapace is a dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tortoises, the ...

that cover the entire upper half of the body, and five pairs of uniramous cephalic appendages. Both groups have unbranched

antennules Antennae ( antenna), sometimes referred to as "feelers", are paired appendages used for sensing in arthropods. Antennae are connected to the first one or two segments of the arthropod head. They vary widely in form but are always made of one o ...

and a segmented trunk with

biramous The arthropod leg is a form of jointed appendage of arthropods, usually used for walking. Many of the terms used for arthropod leg segments (called podomeres) are of Latin origin, and may be confused with terms for bones: ''coxa'' (meaning hip, plu ...

appendages. Recent research has suggested the previously enigmatic Cambrian trliobite-like arthropods ''

Skania ''Skania'' is a Middle Cambrian fossil arthropod that is closely related to the Early Cambrian ''Primicaris'' from the Chengjiang Biota, China. It bears a superficial resemblance to the Ediacaran The Ediacaran Period ( ) is a geological ...

'' and ''

Primicaris ''Primicaris'' is genus of Cambrian arthropod from the Chengjiang biota of China and the Burgess Shale of Canada. It contains a single described species, ''P. larvaformis''. Its specimens were once thought to be meraspids of '' Naraoia spinosa'' ...

'' may belong to this group. Their phylogenetic position is uncertain, various studies have alternatively placed them within in the

Arachnomorpha Arachnomorpha is a proposed subdivision or clade of Arthropoda, comprising the group formed by the trilobites and their close relatives ( Artiopoda), Megacheira (which may be paraphyletic) and chelicerates. Under this proposed classification ...

as relatives of

Artiopoda The Artiopoda is a grouping of extinct arthropods that includes trilobites and their close relatives. It was erected by Hou and Bergström in 1997 to encompass a wide diversity of arthropods that would traditionally have been assigned to the Trilo ...

(

trilobites Trilobites (; meaning "three lobes") are extinct marine arthropods that form the class Trilobita. Trilobites form one of the earliest-known groups of arthropods. The first appearance of trilobites in the fossil record defines the base of the ...

and kin), as

stem-group In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor. ...

Mandibulata Mandibulata, termed "mandibulates", is a clade of arthropods that comprises the extant subphyla Myriapoda (millipedes and others), Crustacea and Hexapoda (insects and others). Mandibulata is currently believed to be the sister group of the clade ...

, or as stem group euarthropods.

Taxonomy

After Moysiuk et al, 2022. * Acercostraca ** ?''

, Canada,

(

Miaolingian The Miaolingian is the third Series of the Cambrian Period, and was formally named in 2018. It lasted from about to million years ago and is divided in ascending order into 3 stages: the Wuliuan, Drumian, and Guzhangian. The Miaolingian is pre ...

) ? Kaili Formation, China, Cambrian (

Wuliuan The Wuliuan stage is the fifth stage of the Cambrian, and the first stage of the Miaolingian Series of the Cambrian. It was formally defined by the ICS in 2018. Its base is defined by the first appearance of the trilobite species '' Oryctocepha ...

) ** ?''

'' Burgess Shale, Canada, Cambrian (Miaolingian),

Maotianshan Shales The Maotianshan Shales are a series of Early Cambrian deposits in the Chiungchussu Formation, famous for their '' Konservat Lagerstätten'', deposits known for the exceptional preservation of fossilized organisms or traces. The Maotianshan Shale ...

, China,

Cambrian Stage 3 Cambrian Stage 3 is the still unnamed third stage of the Cambrian. It succeeds Cambrian Stage 2 and precedes Cambrian Stage 4, although neither its base nor top have been formally defined. The plan is for its lower boundary to correspond approxi ...

** Vachonisiidae *** ''

Xylokorys ''Xylokorys'' is a genus of marrellomorph known from two specimens from the Silurian The Silurian ( ) is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at million years ago ( Mya), to the b ...

'' Coalbrookdale Formation, England,

Silurian The Silurian ( ) is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at million years ago (Mya), to the beginning of the Devonian Period, Mya. The Silurian is the shortest period of the Paleozoi ...

(

Wenlock Wenlock may refer to: Places United Kingdom * Little Wenlock, a village in Shropshire * Much Wenlock, a town in Shropshire ** (Much) Wenlock (UK Parliament constituency) ** Wenlock Priory, a 7th/12th-century monastery * Wenlock Basin, a canal basi ...

) *** ''

Vachonisia ''Vachonisia'' is a Devonian marrellomorph known from the Lower Devonian Hunsrück Slate. It grows in a similar fashion to the other Hunsruck marrellomorph, ''Mimetaster'', and is closely related to the Silurian ''Xylokorys''. It is known fro ...

Hunsrück Slate The Hunsrück () is a long, triangular, pronounced upland in Rhineland-Palatinate, Germany. It is bounded by the valleys of the Moselle-Saar (north-to-west), the Nahe (south), and the Rhine (east). It is continued by the Taunus mountains, past t ...

, Germany, Lower

Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, w ...

(

Emsian The Emsian is one of three faunal stages in the Early Devonian Epoch. It lasted from 407.6 ± 2.6 million years ago to 393.3 ± 1.2 million years ago. It was preceded by the Pragian Stage and followed by the Eifelian Stage. It is named after ...

) *** '' Enosiaspis''

Fezouata Formation The Fezouata Formation or Fezouata Shale is a geological formation in Morocco which dates to the Early Ordovician.

, Morocco, Early

Ordovician The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. ...

(

Floian The Floian is the second stage of the Ordovician Period. It succeeds the Tremadocian with which it forms the Lower Ordovician epoch. It precedes the Dapingian Stage of the Middle Ordovician. The Floian extended from to million years ago. The ...

) * Marrellida ** ''

Balang Formation The Balang formation, is a Cambrian Period geological formation, which outcrops in western Hunan and eastern Guizhou in southern China. It contains Burgess Shale-type soft-bodied fossils. It is intermediate in age between the Chengjiang and Ka ...

, China,

Cambrian Stage 4 Cambrian Stage 4 is the still unnamed fourth stage of the Cambrian and the upper stage of Cambrian Series 2. It follows Cambrian Stage 3 and lies below the Wuliuan. The lower boundary has not been formally defined by the International Commissio ...

Kaili Formation, China, Cambrian (Wuliuan), Burgess Shale, Canada, Cambrian (Miaolingian) ** '' Furca'' Letná Formation'','' Czech Republic, Upper Ordovician (

Sandbian The Sandbian is the first stage of the Upper Ordovician. It follows the Darriwilian and is succeeded by the Katian. Its lower boundary is defined as the first appearance datum of the graptolite species '' Nemagraptus gracilis'' around million ye ...

) ** "Furca" mauretanica (''

nomen nudum In taxonomy, a ''nomen nudum'' ('naked name'; plural ''nomina nuda'') is a designation which looks exactly like a scientific name of an organism, and may have originally been intended to be one, but it has not been published with an adequate des ...

'') Fezouata Formation, Morocco, Early Ordovician (Floian) ** ''"Mimetaster" florestaensis''

Floresta Formation The Floresta Formation ( es, Formación Floresta, Df) is a geological formation of the Altiplano Cundiboyacense in the Eastern Ranges of the Colombian Andes. The sequence of siltstones, shales, coquinas and sandstone beds dates to the Devonian ...

Argentina, Lower Ordovician (

Tremadocian The Tremadocian is the lowest stage of Ordovician. Together with the later Floian Stage it forms the Lower Ordovician Epoch. The Tremadocian lasted from to million years ago. The base of the Tremadocian is defined as the first appearance of the ...

) ** Mimetasteridae *** ''

Tomlinsonus ''Tomlinsonus'' is an extinct genus of marellomorph arthropod known from the Late Ordovician ( Katian) Kirkfield Formation of Ontario, Canada. It is a member of Marellida, and closely related to '' Mimetaster''. Description Only a single pa ...

Kirkfield Formation Kirkfield is a village located in the city of Kawartha Lakes, in the Canadian province of Ontario. The unincorporated village was named in 1864 after the initial name, ''Novar'', was rejected by the government. A list of 8 possible choices was the ...

, Canada, Late Ordovician (

Katian The Katian is the second stage of the Upper Ordovician. It is preceded by the Sandbian and succeeded by the Hirnantian Stage. The Katian began million years ago and lasted for about 7.8 million years until the beginning of the Hirnantian million ...

) *** ''

Mimetaster ''Mimetaster'' is an extinct genus of Marrellomorpha, marrellomorph arthropod. The type species, ''Mimetaster hexagonalis'' is known from the Lower Devonian (Pragian-Emsian) Hunsrück Slate, and amongst the most common arthropods from the locality ...

, Germany, Lower

(

) Fragmentary taxa assigned to Marrelomorpha include ''

Austromarrella ''Austromarrella'' is an extinct genus of marrellomorph arthropod known from the Middle Cambrian (late Templetonian to early Floran) of Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign cou ...

'' from

Cambrian Series 3 The Miaolingian is the third Series of the Cambrian Period, and was formally named in 2018. It lasted from about to million years ago and is divided in ascending order into 3 stages: the Wuliuan, Drumian, and Guzhangian. The Miaolingian is pr ...

aged deposits in Australia, and '' Dyrnwynia'' from the Ordovician (

Darriwilian The Darriwilian is the upper stage of the Middle Ordovician. It is preceded by the Dapingian and succeeded by the Upper Ordovician Sandbian Stage. The lower boundary of the Darriwilian is defined as the first appearance of the graptolite species ...

) aged

Llanfallteg Formation The Llanfallteg Formation is a geologic formation in Wales. It preserves fossils dating back to the Ordovician period. It predominantly consists of ash containing siltstones, as wells as ash fall deposits and tuffs. It likely dates to the Darriw ...

of Wales, which in its original description was assigned to Marrelida.

Gallery

References

Paleozoic arthropods Arthropod classes {{paleo-arthropod-stub