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. 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 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 appendages on the cephalon, 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 Trunk may refer to: Biology * Trunk (anatomy), synonym for torso * Trunk (botany), a tree's central superstructure * Trunk of corpus callosum, in neuroanatomy * Elephant trunk, the proboscis of an elephant Computing * Trunk (software), in rev ...

with biramous 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 as relatives of Artiopoda ( trilobites and kin), as stem-group Mandibulata, or as stem group euarthropods.

Taxonomy

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

, Canada,

( Miaolingian) ? Kaili Formation, China, Cambrian ( Wuliuan) ** ?''

'' 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, 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) *** '' 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) * Marrellida ** '' Marrella'' Balang Formation, 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) ** "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 Argentina, Lower Ordovician ( Tremadocian) ** 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, Canada, Late Ordovician ( Katian) *** ''

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 ...

'' Hunsrück Slate, Germany, Lower

( Emsian) 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 aged deposits in Australia, and '' Dyrnwynia'' from the Ordovician ( Darriwilian) aged Llanfallteg Formation of Wales, which in its original description was assigned to Marrelida.

Gallery

References

Paleozoic arthropods Arthropod classes {{paleo-arthropod-stub