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Lobopodians are members of the informal group Lobopodia, or the formally erected phylum Lobopoda Cavalier-Smith (1998). They are panarthropods with stubby legs called lobopods, a term which may also be used as a common name of this group as well. While the definition of lobopodians may differ between literatures, it usually refers to a group of soft-bodied, marine worm-like fossil panarthropods such as Aysheaia and Hallucigenia.
Opabinia regalis is an extinct, stem group arthropod found in the Middle Cambrian Burgess Shale Lagerstätte of British Columbia. Opabinia was a soft-bodied animal, measuring up to 7 cm in body length, and its segmented trunk had flaps along the sides and a fan-shaped tail. The head shows unusual features: five eyes, a mouth under the head and facing backwards, and a clawed proboscis that probably passed food to the mouth. Opabinia probably lived on the seafloor, using the proboscis to seek out small, soft food. Fewer than twenty good specimens have been described; 3 specimens of Opabinia are known from the Greater Phyllopod bed, where they constitute less than 0.1% of the community.
Aysheaia is an extinct genus of soft-bodied lobopodian, known from the Middle Cambrian Burgess Shale of British Columbia, Canada
Protichnites is an ichnogenus of trace fossil consisting of the imprints made by the walking activity of certain arthropods. It consists of two rows of tracks and a medial furrow between the two rows. This furrow, which may be broken, set at an angle, and of varying width and depth, is thought to be the result of the tail region contacting the substrate.
Cheloniellida is a taxon of extinct Paleozoic arthropods. As of 2018, 7 monotypic genera of cheloniellids had been formally described, whose fossils are found in marine strata ranging from Ordovician to Devonian in age. Cheloniellida has a controversial phylogenetic position, with previous studies associated it as either a member or relative of various fossil and extant arthropod taxa. It was later accepted as a member of Vicissicaudata within Artiopoda.
Aglaspidida is an extinct order of aquatic arthropods that were once regarded as primitive chelicerates. However, anatomical comparisons demonstrate that the aglaspidids cannot be accommodated within the chelicerates, and that they lie instead within the Artiopoda, thus placing them closer to the trilobites. Aglaspidida contains the subgroups Aglaspididae and Tremaglaspididae, which are distinguished by the presence of acute/spinose genal angles and a long spiniform tailspine in the Aglaspididae.
Arthropods are invertebrate animals in the phylum Arthropoda. They possess an exoskeleton with a cuticle made of chitin, often mineralised with calcium carbonate, a segmented body, and paired jointed appendages. In order to keep growing, they must go through stages of moulting, a process by which they shed their exoskeleton to reveal a new one. They are an extremely diverse group, with up to 10 million species.
Tuzoia is an extinct genus of large bivalved arthropod known from Early to Middle Cambrian marine environments from what is now North America, Australia, China, Europe and Siberia. The large, domed carapace reached lengths of 180 millimetres (7.1 in), making them amongst the largest known Cambrian arthropods.
Marrellomorpha are an extinct group of arthropods known from the Cambrian 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 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 that cover the entire upper half of the body, and five pairs of uniramous cephalic appendages. Both groups have unbranched antennules and a segmented trunk with biramous appendages. Recent research has suggested the previously enigmatic Cambrian trliobite-like arthropods Skania and Primicaris belong to this group. Their phylogenetic position is uncertain, various studies have alternatively placed them within in the Arachnomorpha as relatives of Artiopoda, as related to Mandibulata, or as stem group euarthropods.
Kodymirus is a genus of Early Cambrian arthropod, known from the Czech Republic, which bears some resemblance to eurypterids and aglaspidids. Although it possessed great appendage-like raptorial arms, it was not homologous with those of megacheirans, and was instead a member of Vicissicaudata, closely related to aglaspidids. It is part of a small and low-diversity Paseky Shale fauna group, which dwelt in brackish waters.
Vladicaris is an arthropod known from the Lower Cambrian Paseky Shale member, Czech Republic, where it occurs alongside other arthropods, namely Kodymirus vagans and Kockurus grandis. It has been attributed to the Crustacea, and if it does indeed belong in the crown group of that subphylum, it would be the earliest known representative of the group. Its position within the Crustacea is unclear – it has been allied with the Phyllocarida and the Branchiopoda.
Australaglaspis stoneyensis is an aglaspid that superficially resembles a horseshoe crab, or trilobite. It is known from Idamean-aged strata at Stoney Point in north-west Tasmania.
Beckwithia is an extinct genus of average to large size, soft bodied artiopodan arthropods that lived during the late Middle and Upper Cambrian on the former paleocontinent Laurentia, in what are now Utah and Wisconsin. It has an inverted egg-shape, with a semi-circular head, 11 abdominal segments and a tail spine. It is a typical member of the group Aglaspidida.
Paleontology in Wisconsin refers to paleontological research occurring within or conducted by people from the U.S. state of Wisconsin. The state has fossils from the Precambrian, much of the Paleozoic, and the later part of the Cenozoic. Most of the Paleozoic rocks are marine in origin. Because of the thick blanket of Pleistocene glacial sediment that covers the rock strata in most of the state, Wisconsin’s fossil record is relatively sparse. In spite of this, certain Wisconsin paleontological occurrences provide exceptional insights concerning the history and diversity of life on Earth.
Cyclopites is a genus of aglaspidid arthropods that lived in shallow seas in what is now Wisconsin during Late Cambrian times. It is distinguished from other aglaspidids by the extreme proximity of its eyes. The genus earns its name from this presence of what might appear to be a single, central eye.
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 Trilobitomorpha. Trilobites, in part due to their mineralising exoskeletons, are by far the most diverse and long lived members of the clade, with most records of other members, which lack mineralised exoskeletons, being from Cambrian deposits.
Strabops is a genus of strabopid, an extinct group of arthropods. Strabops is known from a single specimen from the Late Cambrian of the Potosi Dolomite, Missouri, collected by a former professor, Arthur Thacher. It is classified in the family Strabopidae of the monotypic order Strabopida, a group closely related to the aglaspidids with uncertain affinities. The generic name is composed by the Ancient Greek words στραβός, meaning "squinting", and ὄψῐς, meaning "face".
Strabopidae is the only family of the order Strabopida, an extinct group of arthropods known from the Cambrian period.
Paleomerus is a genus of strabopid, a group of extinct arthropods. It has been found in deposits from the Cambrian period. It is classified in the family Strabopidae of the monotypic order Strabopida. It contains two species, P. hamiltoni from Sweden and P. makowskii from Poland. The generic name is composed by the Ancient Greek words παλαιός (palaiós), meaning "ancient", and μέρος (méros), meaning "part".
Erratus is an extinct genus of marine arthropod from the Cambrian of China. Its type and only species is Erratus sperare. Erratus is likely one of the most basal known arthropods, and its discovery has helped scientists understand the early evolution of arthropod trunk appendages. Some of the stem-arthropods like radiodonts did not have legs, instead they had flap like appendages that helped them swim. Erratus on the other hand had not only flaps but also a set of primitive legs. It also supported the theory that the gills of aquatic arthropods probably evolved into the wings and lungs of terrestrial arthropods later in the Paleozoic.
References
- 1 2 Chlupáč, I. "Lower Cambrian arthropods from the Paseky Shale (Barrandian area, Czech Republic)". Journal of the Czech Geological Society . 40 (4): 9–36. Retrieved 2012-08-21.
- ↑ Van Roy, P. (2005). "An aglaspidid arthropod from the Upper Ordovician of Morocco with remarks on the affinities and limitations of Aglaspidida". Transactions of the Royal Society of Edinburgh: Earth Sciences. 96 (4): 327. doi:10.1017/S0263593300001334.
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