Panarthropoda

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Panarthropoda
Temporal range: Cambrian - Recent
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Molecular clock and ichnofossils indicate a possible Ediacaran origin [1] [2]
Peripatopsis lawrencei 134803788 (cropped).jpg
Panarthropods include onychophorans such as Peripatopsis and arthropods such as polydesmid millipedes
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Clade: ParaHoxozoa
Clade: Bilateria
Clade: Nephrozoa
(unranked): Protostomia
Superphylum: Ecdysozoa
(unranked): Panarthropoda
Nielsen, 1995
Phyla

Panarthropoda is a proposed animal clade containing the extant phyla Arthropoda, Tardigrada (water bears) and Onychophora (velvet worms). [3] Panarthropods also include extinct marine legged worms known as lobopodians ("Lobopodia"), a paraphyletic group where the last common ancestor and basal members (stem-group) of each extant panarthropod phylum are thought to have risen. [4] [5] [6] [7] [8] [9] However the term "Lobopodia" is sometimes expanded to include tardigrades and onychophorans as well. [5]

Contents

Common characteristics of the Panarthropoda include a segmented body, paired ladder-like ventral nervous system, and the presence of paired appendages correlated with body segments. [10] [5] [6] [8]

Taxonomy

Bilateria

Not all studies support the monophyly of Panarthropoda, [11] but most do, including neuroanatomical, [12] phylogenomic [10] [13] [14] and palaeontological [15] [4] [5] [6] studies. At least a close relationship between onychophorans and arthropods is widely agreed upon, but the position of tardigrades is more controversial. [16] Some phylogenomic studies have found tardigrades to be more closely related to nematodes. [17] [18] Traditionally, panarthropods were considered to be closely related to the annelids, grouped together as the Articulata (animals with body segments), but subsequent phylogenomic studies consistently place them closer to cycloneuralians (nematodes, nematomorphs, loriciferans, kinorhynchas & priapulids), grouped together as Ecdysozoa. [19] [20] [13] [14] While annelids are placed among the Spiralia (making them more closely related to mollusks, flatworms and such), [20] having evolved their segmented bodies convergently. [21]

Interrelationship

Panarthropoda

(Lobopodian taxa controversial)*

(Lobopodian taxa controversial)*

(Lobopodian taxa controversial)*

Crown-group Tardigrada SEM image of Milnesium tardigradum in active state - journal.pone.0045682.g001-2.png

Summarized interrelationship of Panarthropoda, with focus on phylogeny between lobopodians (asterisk) and extant panarthropods (bold). Relationship between the total-group of extant panarthropods is unresolve (see text for discussion). [5] [6]

There are three competing hyphotheses for the interrelationship between the extant panarthropod phyla, each known as Tactopoda (Arthropoda+Tardigrada), Antennopoda (Arthropoda+Onychophora), and the sister relationship between Onychophora and Tardigrada (Lobopodia sensu Smith & Goldstein 2017). [22]

Panarthropoda

Arthropoda

Lobopodia
sensu Smith & Goldstein 2017

Tactopoda had been supported by mitochondrial gene arrangements, [23] palaeontological [24] [4] and neuroanatomical evidences, specifically the presence of segmented ganglia shared by arthropods and tardigrades. [25] Antennopodia united by the presence of specialized head appendages and deutocerebrum (additional second section of the brain), but subsequent anatomical studies suggest these features were convergently evolved between onychophoran and arthropod lineages. [15] [26] Onychophorans and tardigrades shared some lobopodian traits (e.g. soft cuticle, lobopodous appendages and peripheral nerve roots), but these were generally considered to be plesiomorphies traced back to the last common ancestor of Panarthropoda or Ecdysozoa. [4] [5] [27] [6] While most phylogenomic analyses support the monophyly of Panarthropoda, the results of interrelationship between the three phyla are less correlated - some of them inconsistently placing Tardigrada within Arthropoda, [10] while the others mostly recovering either Antennopoda or Onychophora+Tardigrada. [10] [13] [14]

Within extinct lobopodians, at least Antennacanthopodia are widely accepted as part of the onychophoran stem-group. [28] [4] [29] [30] [31] [27] [32] [33] [6] [34] [35] ‹The template Excessive citations inline is being considered for deletion.› [ excessive citations ] On the other hand, siberiids ( Siberion , Megadictyon and Jianshanopodia ) and gilled lobopodians ( Pambdelurion and Kerygmachela ) represent transitional forms between typical lobopodians and basal arthropods (e.g. Opabinia and Radiodonta). [28] [4] [29] [30] [31] [27] [32] [5] [6] [33] [34] [7] [8] [35] [36] [9] ‹The template Excessive citations inline is being considered for deletion.› [ excessive citations ] The positions of most other lobopodians (e.g. Hallucigenia and luolishaniids as stem onychophorans [4] [29] [30] [31] [27] [32] [35] ‹The template Excessive citations inline is being considered for deletion.› [ excessive citations ] or stem panarthropods [33] [34] [36] ), including the lobopodian members of tardigrade stem-group (represented by Onychodictyon ferox [4] [29] [30] [31] [27] [32] [35] ‹The template Excessive citations inline is being considered for deletion.› [ excessive citations ] or Aysheaia [33] [34] [36] ) are more controversial.

Sialomorpha , a genus of microinvertebrate discovered in Dominican amber in 2019, is also considered to be a panarthropod. However, due to the unusual combination of tardigrade and mite-like characteristics, its exact placement is uncertain. [37]

See also

Related Research Articles

<span class="mw-page-title-main">Lobopodia</span> Group of extinct worm-like animals with legs

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. However, other genera like Kerygmachela and Pambdelurion are often referred to as “gilled lobopodians”.

<span class="mw-page-title-main">Onychophora</span> Phylum of invertebrate animals

Onychophora, commonly known as velvet worms or more ambiguously as peripatus, is a phylum of elongate, soft-bodied, many-legged animals. In appearance they have variously been compared to worms with legs, caterpillars, and slugs. They prey upon other invertebrates, which they catch by ejecting an adhesive slime. Approximately 200 species of velvet worms have been described, although the true number of species is likely greater. The two extant families of velvet worms are Peripatidae and Peripatopsidae. They show a peculiar distribution, with the peripatids being predominantly equatorial and tropical, while the peripatopsids are all found south of the equator. It is the only phylum within Animalia that is wholly endemic to terrestrial environments, at least among extant members. Velvet worms are generally considered close relatives of the Arthropoda and Tardigrada, with which they form the proposed taxon Panarthropoda. This makes them of palaeontological interest, as they can help reconstruct the ancestral arthropod. Only two fossil species are confidently assigned as onychophorans: Antennipatus from the Late Carboniferous, and Cretoperipatus from the Late Cretaceous, the latter belonging to Peripatidae. In modern zoology, they are particularly renowned for their curious mating behaviours and the bearing of live young in some species.

<i>Hallucigenia</i> Genus of Cambrian animals

Hallucigenia is a genus of lobopodian known from Cambrian aged fossils in Burgess Shale-type deposits in Canada and China, and from isolated spines around the world. The generic name reflects the type species' unusual appearance and eccentric history of study; when it was erected as a genus, H. sparsa was reconstructed as an enigmatic animal upside down and back to front. Lobopodians are a grade of Paleozoic panarthropods from which the velvet worms, water bears, and arthropods arose.

<i>Opabinia</i> Extinct stem-arthropod species found in Cambrian fossil deposits

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.

<i>Aysheaia</i> Extinct genus of soft-bodied animals

Aysheaia is an extinct genus of soft-bodied lobopodian, known from the Middle Cambrian Burgess Shale of British Columbia, Canada

<span class="mw-page-title-main">Ecdysozoa</span> Superphylum of protostomes including arthropods, nematodes and others

Ecdysozoa is a group of protostome animals, including Arthropoda, Nematoda, and several smaller phyla. The grouping of these animal phyla into a single clade was first proposed by Eernisse et al. (1992) based on a phylogenetic analysis of 141 morphological characters of ultrastructural and embryological phenotypes. This clade, that is, a group consisting of a common ancestor and all its descendants, was formally named by Aguinaldo et al. in 1997, based mainly on phylogenetic trees constructed using 18S ribosomal RNA genes.

<span class="mw-page-title-main">Dinocaridida</span> Extinct class of basal arthropods

Dinocaridida is a proposed fossil taxon of basal arthropods, which flourished during the Cambrian period and survived up to Early Devonian. Characterized by a pair of frontal appendages and series of body flaps, the name of Dinocaridids refers to the suggested role of some of these members as the largest marine predators of their time. Dinocaridids are occasionally referred to as the 'AOPK group' by some literatures, as the group compose of Radiodonta, Opabiniidae, and the "gilled lobopodians" Pambdelurion and Kerygmachelidae. It is most likely paraphyletic, with Kerygmachelidae and Pambdelurion more basal than the clade compose of Opabiniidae, Radiodonta and other arthropods.

<i>Pambdelurion</i> Extinct genus of Arthropod

Pambdelurion is an extinct genus of panarthropod from the Cambrian aged Sirius Passet site in northern Greenland. Like the morphologically similar Kerygmachela from the same locality, Pambdelurion is thought to be closely related to arthropods, combining characteristics of "lobopodians" with those of primitive arthropods.

<span class="mw-page-title-main">Tardigrade</span> Phylum of microscopic animals, also known as water bears

Tardigrades, known colloquially as water bears or moss piglets, are a phylum of eight-legged segmented micro-animals. They were first described by the German zoologist Johann August Ephraim Goeze in 1773, who called them Kleiner Wasserbär. In 1777, the Italian biologist Lazzaro Spallanzani named them Tardigrada, which means "slow steppers".

<span class="mw-page-title-main">Radiodonta</span> Extinct order of basal arthropods

Radiodonta is an extinct order of stem-group arthropods that was successful worldwide during the Cambrian period. They may be referred to as radiodonts, radiodontans, radiodontids, anomalocarids, or anomalocaridids, although the last two originally refer to the family Anomalocarididae, which previously included all species of this order but is now restricted to only a few species. Radiodonts are distinguished by their distinctive frontal appendages, which are morphologically diverse and used for a variety of functions. Radiodonts included the earliest large predators known, but they also included sediment sifters and filter feeders. Some of the most famous species of radiodonts are the Cambrian taxa Anomalocaris canadensis, Hurdia victoria, Peytoia nathorsti, Titanokorys gainessii, Cambroraster falcatus and Amplectobelua symbrachiata. The later surviving members include the subfamily Aegirocassisinae from the Early Ordovician of Morocco and the Early Devonian member Schinderhannes bartelsi from Germany.

<i>Diania</i> Extinct genus of Cambrian animals

Diania is an extinct genus of lobopodian panarthropod found in the Lower Cambrian Maotianshan shale of China, represented by a single species - D. cactiformis. Known during its investigation by the nickname "walking cactus", this organism belongs to a group known as the armoured lobopodians, and has a simple worm-like body with robust, spiny legs. Initially, the legs were thought to have a jointed exoskeleton and Diania was suggested to be evolutionarily close to early arthropods, but many later studies have rejected this interpretation.

<span class="mw-page-title-main">Luolishaniidae</span> Extinct family of worm-like animals

The Luolishaniidae or Luolishaniida are a group of Cambrian and Ordovician lobopodians with anterior 5 or 6 pairs of setiferous lobopods. Most luolishaniids also have posterior lobopods each with a hooked claws, and thorn-shaped sclerites arranged as three or more per trunk segment. The type genus is based on Luolishania longicruris Hou and Chen, 1989, from the Chengjiang Lagerstatte, South China. They are presumed to have been benthic suspension or filter feeders.

<span class="mw-page-title-main">Tactopoda</span> Group of ecdysozoan animals

Tactopoda or Arthropodoidea is a proposed clade of ecdysozoan animals that includes the phyla Tardigrada and Euarthropoda, supported by various morphological observations. The cladogram below shows the relationships implied by this hypothesis.

<i>Cardiodictyon</i> Extinct genus of lobopodians

Cardiodictyon is a genus of lobopodian known from 518 millions years old Chengjiang Lagerstätte. 525 millions years old partial fossil is also reported. It has ~25 pairs of legs, each associated with a pair of dorsal plates.

<i>Euperipatoides kanangrensis</i> Species of velvet worm

Euperipatoides kanangrensis is a species of velvet worm of the Peripatopsidae family, described in 1996 from specimens collected in Kanangra-Boyd National Park, New South Wales. This species has 15 pairs of legs in both sexes. It is endemic to Australia. The embryonic development of Euperipatoideskanangrensis has been described. This species is viviparous. This species is used as model organism for the last common ancestor of the Panarthropoda. It resembles fossil Cambrian lobopodians.

<i>Acinocricus</i> Extinct genus of lobopodians

Acinocricus is a genus of extinct panarthropod belonging to the group Lobopodia and known from the middle Cambrian Spence Shale of Utah, United States. As a monotypic genus, it has one species Acinocricus stichus. The only lobopodian discovered from the Spence Shale, it was described by Simon Conway Morris and Richard A. Robison in 1988. Owing to the original fragmentary fossils discovered since 1982, it was initially classified as an alga, but later realised to be an animal belonging to Cambrian fauna.

Luolishania is an extinct genus of lobopodian panarthropod and known from the Lower Cambrian Chiungchussu Formation of the Chengjiang County, Yunnan Province, China. A monotypic genus, it contains one species Luolishania longicruris. It was discovered and described by Hou Xian-Guang and Chen Jun-Yuan in 1989. It is one of the superarmoured Cambrian lobopodians suspected to be either an intermediate form in the origin of velvet worms (Onychophora) or basal to at least Tardigrada and Arthropoda. It is the basis of the family name Luolishaniidae, which also include other related lobopods such as Acinocricus, Collinsium, Facivermis, and Ovatiovermis. Along with Microdictyon, it is the first lobopodian fossil discovered from China.

Carbotubulus is a genus of extinct worm belonging to the group Lobopodia and known from the Carboniferous Carbondale Formation of the Mazon Creek area in Illinois, US. A monotypic genus, it contains one species Carbotubulus waloszeki. It was discovered and described by Joachim T. Haug, Georg Mayer, Carolin Haug, and Derek E.G. Briggs in 2012. With an age of about 300 million years, it is the first long-legged lobopodian discovered after the period of Cambrian explosion.

<span class="mw-page-title-main">Deuteropoda</span> Clade of arthropods

Deuteropoda is a proposed clade of arthropods whose members are distinguished from more basal stem-group arthropods like radiodonts by an anatomical reorganization of the head region, namely the appearance of a differentiated first appendage pair, a multisegmented head, a hypostome/labrum complex, and by bearing pairs of segmented biramous limbs.

<span class="mw-page-title-main">Antennopoda</span> Proposed clade of animals

The Antennopoda are a proposed clade consisting of the Euarthropoda and the Onychophora, as sister of the Tardigrada, together forming the Panarthropoda. Stanleycaris appears to be a basal Euarthropod.

References

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