Lobopodia
Template:Short description Template:About Template:Paraphyletic groupLobopodians are members of the informal group Lobopodia<ref>Template:Cite journal</ref> (Template:Etymology),Template:Citation needed or the formally erected phylum Lobopoda Cavalier-Smith (1998).<ref name="Cavalier-Smith">Template:Cite journal</ref> They are panarthropods with stubby legs called lobopods,<ref name=":0">Template:Cite journal</ref> a term which may also be used as a common name of this group as well.<ref name=":16">Template:Cite journal</ref><ref name="Liu2006"/> While the definition of lobopodians may differ between literatures,<ref name=":8" /> it usually refers to a group of soft-bodied, marine (and freshwater) worm-like fossil panarthropods such as Aysheaia and Hallucigenia.<ref name="Knecht2025" /> However, other genera like Kerygmachela and Pambdelurion (which have features similar to other groups) are often referred to as "gilled lobopodians".<ref>Template:Cite journal</ref><ref name=":0" /><ref name=":13" />
The oldest near-complete fossil lobopodians date to the Lower Cambrian; some are also known from Ordovician, Silurian and Carboniferous Lagerstätten.<ref>Template:Cite journal</ref><ref name="vonBitter2007">Template:Cite journal</ref><ref name=":35">Template:Cite journal</ref><ref name=Knecht2025/> Some bear toughened claws, plates or spines, which are commonly preserved as carbonaceous or mineralized microfossils in Cambrian strata.<ref name=":15">Template:Cite journal</ref><ref name=":26">Template:Cite journal</ref> The grouping is considered to be paraphyletic, as the three living panarthropod groups (Arthropoda, Tardigrada and Onychophora) are thought to have evolved from lobopodian ancestors.
Definitions
The lobopodian concept varies from author to author.<ref name=":8" /> Its most general sense refers to a suite of mainly Cambrian worm-like panarthropod taxa possessing lobopods – for example, Aysheaia, Hallucigenia, and Xenusion – which were traditionally united as "Xenusians" or "Xenusiids" (class Xenusia).<ref name=":19" /><ref name=":30" /><ref name=":31">Template:Cite journal</ref> Certain Dinocaridid genera, such as Opabinia, Pambdelurion, and Kerygmachela, may also be regarded as lobopodians,<ref name=":1">Template:Cite journal</ref><ref name=":13"/> sometimes referred to more specifically as "gilled lobopodians" or "gilled lobopods".<ref name=":18">Template:Cite journal</ref> This traditional, informal usage of "Lobopodia" treats it as an evolutionary grade, including only extinct Panarthropods near the base of crown Panarthropoda. Crown Panarthropoda comprises the three extant Panarthropod phyla – Onychophora (velvet worms), Tardigrada (waterbears), and Arthropoda (arthropods) – as well as their most recent common ancestor and all of its descendants. Thus, in this usage, Lobopodia consists of various basal Panarthropods.<ref name=":0" /><ref name="ReferenceA">Template:Cite journal</ref><ref name=":2"/><ref name=":8"/><ref name=":10">Template:Cite journal</ref><ref name=":11" /> This corresponds to "A" in the image to the left.
An alternative, broader definition of Lobopodia would also incorporate Onychophora and Tardigrada,<ref name=":19">Template:Cite journal</ref><ref name=":1"/><ref name="Cavalier-Smith"/> the two living panarthropod phyla which still bear lobopodous limbs. This definition, corresponding to "C", is a morphological one, depending on the superficial similarity of appendages (the "lobopods"). Thus, it is paraphyletic, excluding the euarthropods, which are descendants of certain lobopodians, on the basis of their highly divergent limb morphology.<ref name=":0" /> "Lobopodia" has also been used to refer to a proposed sister clade to Arthropoda, consisting of the extant Onychophora and Tardigrada, as well as their most recent common ancestor and all of its descendants. This definition renders Lobopodia a monophyletic taxon, if indeed it is valid (that is, if Tardigrades and Onychophora are closer to one another than either is to Arthropoda), but would exclude all the euarthropod-line taxa traditionally considered lobopodians. Its validity is uncertain, however, as there are a number of hypotheses regarding the internal phylogeny of Panarthropoda.<ref>Template:Cite journal</ref> The broadest definition treats Lobopodia as a monophyletic superphylum equivalent in circumscription to Panarthropoda. By this definition, represented by "D" in the image, Lobopodia is no longer treated as an evolutionary grade but as a clade, containing not only the early, superficially "lobopodian" forms but also all of their descendants, including the extant Panarthropods.<ref name=":20">Template:Cite book</ref><ref name=":16" />
Lobopodia has, historically, sometimes included Pentastomida,<ref name=":9" /> a group of parasitic panarthropods which were traditionally thought to be a unique phylum,<ref>Pentastomida - Sociedad Entomológica Aragonesa</ref><ref>Treatise on Zoology - Anatomy, Taxonomy, Biology. The Crustacea, Volum 5</ref> but revealed by subsequent phylogenomic and anatomical studies to be a highly specialized taxon of crustaceans.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref><ref>Template:Cite journal</ref><ref>Template:Cite journal</ref><ref>Template:Citation</ref>
Representative taxa
Template:Multiple image The better-known genera include Aysheaia, which was discovered in the Canadian Burgess Shale, and Hallucigenia, known from both the Chenjiang Maotianshan Shale and the Burgess Shale. Aysheaia pedunculata has a morphology apparently basic for lobopodians<ref name="ReferenceA"/> — for example, a significantly annulated cuticle, a terminal mouth opening, specialized frontalmost appendages, and stubby lobopods with terminal claws. Hallucigenia sparsa is famous for having a complex history of interpretation — it was originally reconstructed with long, stilt-like legs and mysterious fleshy dorsal protuberances, and was long considered a prime example of the way in which nature experimented with the most diverse and bizarre body designs during the Cambrian.<ref>Template:Cite bookTemplate:Page needed</ref> However, further discoveries showed that this reconstruction had placed the animal upside-down: interpreting the "stilts" as dorsal spines made it clear that the fleshy "dorsal" protuberances were actually elongated lobopods. More recent reconstruction even exchanged the front and rear ends of the animal: it was revealed that the bulbous imprint previously thought to be a head was actually gut contents being expelled from the anus.<ref name=":15"/><ref name=":2">Template:Cite journal</ref>
Microdictyon is another charismatic as well as the speciose genus of lobopodians resembling Hallucigenia, but instead of spines, it bore pairs of net-like plates, which are often found disarticulated and are known as an example of small shelly fossils (SSF). Xenusion has the oldest fossil record amongst the described lobopodians, which may trace back to Cambrian Stage 2.<ref name=":19"/><ref name=":13"/> Luolishania is an iconic example of lobopodians with multiple pairs of specialized appendages.<ref name=":4"/> The gill lobopodians Kerygmachela and Pambdelurion shed light on the relationship between lobopodians and arthropods, as they have both lobopodian affinities and characteristics linked to the arthropod stem-group.<ref name=":18"/><ref name=":20"/>
Morphology
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Maximum size of the 3 species of Hallucigenia (from top, H. fortis, H. hongmeia and H. sparsa) in scale.
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Fossils of Xenusion, a lobopodian that might have grown up to 20 centimeters.
Most lobopodians were only a few centimeters in length, while some genera grew up to over 20 centimeters.<ref name="Liu2006"/> Their bodies are annulated, although the presence of annulation may differ between position or taxa, and sometimes difficult to discern due to their close spacing and low relief on the fossil materials.<ref name='Hou2004'/> Body and appendages are circular in cross-section.<ref name='Hou2004'/>
Head
Due to the usually poor preservation, detailed reconstructions of the head region are only available for a handful of lobopodian species.<ref name=":22" /><ref name=":2" /> The head of a lobopodian is more or less bulbous,<ref name=":0" /> and sometime possesses a pair of pre-ocular, presumely protocerebral<ref name=":10" /> appendages – for example, primary antennae<ref name=":3" /><ref name=":4">Template:Cite journal</ref><ref name=":10" /><ref name=":28">Template:Cite journal</ref> or well-developed frontal appendages,<ref name=":32">Template:Cite journal</ref><ref name=":1" /><ref name="Liu2007" /><ref name="Liu2006" /><ref name=":0"/> which are individualized from the trunk lobopods<ref name=":10" /><ref name=":21">Template:Cite journal</ref> (with the exception of Antennacanthopodia, which have two pairs of head appendages instead of one<ref name=":3" />). Mouthparts may consist of rows of teeth<ref name="Hou2004"/><ref name=":2"/><ref name="Liu2007" /><ref name="Liu2006" /><ref name=":7">Template:Cite journal</ref> or a conical proboscis.<ref name=":22">Template:Cite journal</ref><ref name=":0" /><ref name=":6" /> The eyes may be represented by a single ocellus or by numerous<ref name=":23" /> pairs of simple ocelli,<ref name=":0" /> as has been shown in Luolishania<ref name=":4" /> (=Miraluolishania<ref name=":23">Template:Cite journal</ref><ref name=":27" />), Ovatiovermis,<ref name=":6" /> Onychodictyon,<ref name=":22" /> Hallucigenia,<ref name=":2" /> Facivermis,<ref name=":27" /> and less certainly Aysheaia as well.<ref name=":22" /> However, in gilled lobopodians like Kerygmachela, the eyes are relatively complex reflective patches<ref>Template:Cite journal</ref> that may had been compound in nature.<ref name=":14">Template:Cite journal</ref>
Trunk and lobopods
The trunk is elongated and composed of numerous body segments (somites), each bearing a pair of legs called lobopods<ref name=":0" /> or lobopodous limbs.<ref name=":1" /> The segmental boundaries are not as externally significant as those of arthropods, although they are indicated by heteronomous annulations (i.e., the alternation of annulation density corresponding to the position of segmental boundaries) in some species.<ref name=":33">Chen, J.Y., Zhou, G.Q., Ramsköld, L. (1995a). The Cambrian lobopodian Microdictyon sinicum. Bulletin of the National Museum of Natural Science 5, 1–93 (Taichung, Taiwan).</ref><ref name=":4" /><ref name="ReferenceA" /> The trunk segments may bear other external, segment-corresponding structures such as nodes (e.g. Hadranax,<ref name=":16" /> Kerygmachela<ref name=":1" />), papillae (e.g. Onychodictyon<ref name=":22" />), spine/plate-like sclerites (e.g. armoured lobopodians<ref name=":0" />) or lateral flaps (e.g. gilled lobopodians<ref name=":1" /><ref name=":7" />). One member of Lobopodia, Palaeocampa, has spines which seem to have been poisonous as shown by preserved exudates at their tips, with FTIR (Fourier-transform spectrometry analysis) showing the secretions likely contained aldehydes.<ref name="Knecht2025" /> The trunk may terminate with a pair of lobopods (e.g. Aysheaia, Hallucigenia sparsa)<ref name=":2" /> or a tail-like extension (e.g. Paucipodia, Siberion, Jianshanopodia).<ref name=":33" /><ref name="Hou2004" /><ref name="Liu2006" /><ref name=":9" />
The lobopods are flexible and loosely conical in shape, tapering from the body to tips that may <ref name="ReferenceA" /><ref name=":0" /> or may not <ref name=":3">Template:Cite journal</ref><ref name=":12">Template:Cite journal</ref><ref name=":13">Template:Cite journal</ref> bear claws. The claws, if present, are hardened structures with a shape resembling a hook or gently curved spine.<ref name="Hou2004" /><ref name=":36">Template:Cite journal</ref><ref name=":4" /><ref name="ReferenceA" /><ref name=":0" /> Claw-bearing lobopods usually have two claws, but single claws are known (e.g. posterior lobopods of luolishaniids<ref name=":4" /><ref name=":6" /><ref name=":28" />), as are more than two (e.g. three in Tritonychus,<ref name=":34" /> seven in Aysheaia<ref name=":32" />) depending on its segmental or taxonomical association.<ref name="ReferenceA" /> In some genera, the lobopods bear additional structures such as spines (e.g. Diania<ref name=":12" />), fleshy outgrowths (e.g. Onychodictyon<ref name=":22" />), or tubercules (e.g. Jianshanopodia<ref name="Liu2006" />). There is no sign of arthropodization (development of a hardened exoskeleton and segmental division on panarthropod appendages) in known members of lobopodians, even for those belonging to the arthropod stem-group (e.g. gilled lobopodians and siberiids), and the suspected case of arthropodization on the limbs of Diania<ref name=":24">Template:Cite journal</ref> is considered to be a misinterpretation.<ref name=":12" /><ref name=":13" />
Differentiation (tagmosis) between trunk somites barely occurs, except in hallucigeniids and luolishaniids, where numerous pairs of their anterior lobopods are significantly slender (hallucigeniids) or setose (luolishaniids) in contrast to their posterior counterparts.<ref name=":0" /><ref name=":2" /><ref name=":6" /><ref name=":11" /><ref name=":28" />
Internal structures
The gut of lobopodians is often straight, undifferentiated,<ref name=":5">Template:Cite journal</ref> and sometimes preserved in the fossil record in three dimensions. In some specimens the gut is found to be filled with sediment.<ref name="Hou2004">Template:Cite journal</ref> The gut consists of a central tube occupying the full length of the lobopodian's trunk,<ref name="Liu2006">Template:Cite journal</ref> which does not change much in width - at least not systematically. However, in some groups, specifically the gilled lobopodians and siberiids, the gut is surrounded by pairs of serially repeated, kidney-shaped gut diverticulae (digestive glands).<ref name="Liu2006" /><ref name="Liu2007">Template:Cite journal</ref><ref name=":5" /> In some specimens, parts of the lobopodian gut can be preserved in three dimensions. This cannot result from phosphatisation, which is usually responsible for 3-D gut preservation,<ref name="LeancholiaGuts">Template:Cite journal</ref> because the phosphate content of the guts is under 1%; the contents comprise quartz and muscovite.<ref name="Hou2004" /> The gut of the representative Paucipodia is variable in width, being widest at the centre of the body. Its position in the body cavity is only loosely fixed, so flexibility is possible.
Not much is known about the neural anatomy of lobopodians due to the spare and mostly ambiguous fossil evidence. Possible traces of a nervous system were found in Paucipodia, Megadictyon and Antennacanthopodia.<ref name="Liu2007" /><ref name="Hou2004" /><ref name=":3" /> The first and so far the only confirmed evidence of lobopodian neural structures comes from the gilled lobopodian Kerygmachela in Park et al. 2018 — it presents a brain composed of only a protocerebrum (the frontal-most cerebral ganglion of panarthropods) that is directly connected to the nerves of eyes and frontal appendages, suggesting the protocerebral ancestry of the head of lobopodians as well as the whole Panarthropoda.<ref name=":14" />
In some extant ecdysozoan such as priapulids and onychophorans, there is a layer of outermost circular muscles and a layer of innermost longitudinal muscles. The onychophorans also have a third, intermediate, layer of interwoven oblique muscles. Musculature of the gilled lobopodian Pambdelurion shows a similar anatomy,<ref name=":29" /> but that of the lobopodian Tritonychus shows the opposite pattern: it is the outermost muscles that are longitudinal and the innermost layer that consists of circular muscles.<ref name=":34">Template:Cite journal</ref>
Categories
Based on external morphology, lobopodians may fall under different categories — for example the general worm-like taxa as "xenusiid" or "xenusian"; xenusiid with sclerite as "armoured lobopodians"; and taxa with both robust frontal appendages and lateral flaps as "gilled lobopodians". Some of them were originally defined under a taxonomic sense (e.g. class Xenusia), but neither any of them are generally accepted as monophyletic in further studies.<ref name="ReferenceA" /><ref name=":8" /><ref name=":10" />
Armoured lobopodians
Armoured lobopodians referred to xenusiid lobopodians which bore repeated sclerites such as spine or plates on their trunk (e.g. Hallucigenia, Microdictyon, Luolishania) or lobopods (e.g. Diania). In contrast, lobopodians without sclerites may be referred to as "unarmoured lobopodians".<ref name=":3" /><ref name=":13" /> Function of the sclerites were interpreted as protective armor and/or muscle attachment points.<ref name=":33" /><ref name="Budd2001" /><ref name=":0" /> In some cases, only the disarticulated sclerites of the animal were preserved, which represented as component of small shelly fossils (SSF).<ref name=":33" /><ref name=":15" /> Armoured lobopodians were suggest to be onychophoran-related and may even represent a clade in some previous studies,<ref name="Budd2001" /> but their phylogenetic positions in later studies are controversial. (see text)
Gilled lobopodians
Dinocaridids with lobopodian affinities (due to shared features like annulation and lobopods) are referred to as "gilled lobopodians"<ref name=":8" /><ref name=":7" /><ref name=":29" /> or "gilled lobopods".<ref name=":18" /> These forms sport a pair of flaps on each trunk segment, but otherwise no signs of arthropodization, in contrast to more derived dinocaridids like the Radiodonta that have robust and sclerotized frontal appendages. Gilled lobopodians cover at least four genera: Pambdelurion, Kerygmachela, Utahnax and Mobulavermis.<ref name=":13" /><ref name=":37">Template:Cite journal</ref> Opabinia may also fall under this category in a broader sense,<ref name=":8">Template:Cite journal</ref><ref name=":17">Template:Cite journal</ref> although the presence of lobopods in this genus is not definitively proven.<ref name=":38">Template:Cite journal</ref> Omnidens, a genus known only from Pambdelurion-like mouthparts and distal parts of the frontal appendages, may also be a gilled lobopodian.<ref name=":7" /><ref name="qiongqii">Template:Cite journal</ref> The body flaps may have functioned as both swimming appendages and gills,<ref name=":18" /> and are possibly homologous to the dorsal flaps of radiodonts and exites of Euarthropoda.<ref name=":1" /><ref name=":17" /> Whether these genera were true lobopodians is still contested by some.<ref>Template:Cite journal</ref> However, they are widely accepted as stem-group arthropods just basal to radiodonts.<ref name=":8" /><ref name="ReferenceA" /><ref name=":2" /><ref name=":10" />
Siberion and similar taxa
Siberion, Megadictyon and Jianshanopodia may be grouped as siberiids (order Siberiida),<ref name=":9">Template:Cite journal</ref> jianshanopodians<ref name="ReferenceA" /> or "giant lobopodians"<ref>Template:Cite journal</ref> by some literatures. They are generally large — body length ranging from Template:Cvt<ref name=":9"/><ref name="Liu2007"/> — xenusiid lobopodians with widen trunk, stout trunk lobopods without evidence of claws, and most notably a pair of robust frontal appendages.<ref name=":8"/> With the possible exception of Siberion,<ref name=":9" /><ref name="ReferenceA" /> they also have digestive glands like those of a gilled lobopodian and basal euarthropod.<ref name="Liu2006" /><ref name="Liu2007" /><ref name=":8"/><ref name=":5"/> Their anatomy represent transitional forms between typical xenusiids and gilled lobopodians,<ref name=":9"/> eventually placing them under the basalmost position of arthropod stem-group.<ref name="Liu2006"/><ref name="Liu2007"/><ref name=":8"/><ref name=":10"/>
Paleoecology
Lobopodians possibly occupied a wide range of ecological niches.<ref name=":0" /> Although most of them had undifferentiated appendages and straight gut, which would suggest a simple sediment-feeding lifestyle,<ref name=":0" /> sophisticated digestive glands and large size of gilled lobopodians and siberiids would allow them to consume larger food items,<ref name=":0" /><ref name=":5" /> and their robust frontal appendages may even suggest a predatory lifestyle.<ref name="Liu2006" /><ref name=":5" /> On the other hand, luolishaniids such as Luolishania and Ovatiovermis have elaborate feather-like lobopods that presumably formed 'baskets' for suspension or filter-feeding.<ref name=":4" /><ref name=":6">Template:Cite journal</ref> Lobopods with curved terminal claws may have given some lobopodians the ability to climb on harder substrates like rocks, sponges, or animal carcasses.<ref name=":0" />
Not much is known about the physiology of lobopodians. There is evidence to suggest that lobopodians moult just like other ecdysozoan taxa, but the outline and ornamentation of the harden sclerite did not vary during ontogeny.<ref name=":33" /><ref name=":26" /> The gill-like structures on the body flaps of gilled lobopodians and ramified extensions on the lobopods of Jianshanopodia may provide respiratory function (gills).<ref name=":18" /><ref name="Liu2006" /> Pambdelurion may control the movement of their lobopods in a way similar to onychophorans.<ref name=":29">Template:Cite journal</ref>
Distribution
During the Cambrian, lobopodians displayed a substantial degree of biodiversity. One species is known from each of the Ordovician and Silurian periods,<ref name="vonBitter2007" /><ref>Template:Cite journal</ref> with a few more known from the Carboniferous (Mazon Creek) — this represents the paucity of exceptional lagerstatten in post-Cambrian deposits.
Phylogeny
The overall phylogenetic interpretation on lobopodians has changed dramatically since their discovery and first description.<ref name=":0" /> The reassignments are not only based on new fossil evidence, but also new embryological, neuroanatomical, and genomic (e.g. gene expression, phylogenomics) information observed from extant panarthropod taxa.<ref name=":0" /><ref name=":10" /><ref>Template:Cite journal</ref>
Based on their apparently onychophoran-like morphology (e.g. annulated cuticle, lobopodous appendage with claws), lobopodians were originally thought to be present a group of paleozoic onychophorans.<ref>Template:Cite journal</ref><ref name=":30">Template:Cite journal</ref><ref name=":31" /><ref>Template:Cite journal</ref><ref name=":0" /> This interpretation was challenged after the discovery of lobopodians with arthropod and tardigrade-like characteristics,<ref name=":25">Template:Cite journal</ref> suggesting that the similarity between lobopodians and onychophorans represents deeper panarthropod ancestral traits (plesiomorphies) instead of onychophoran-exclusive characteristics (synapomorphies).<ref name=":11" /> For example, The British palaeontologist Graham Budd sees the Lobopodia as representing a basal grade from which the phyla Onychophora and Arthropoda arose, with Aysheaia comparable to the ancestral plan, and with forms like Kerygmachela and Pambdelurion representing a transition that, via the dinocaridids, would lead to an arthropod body plan.<ref name="Budd2001">Template:Cite journal</ref> Aysheaia's surface ornamentation, if homologous with palaeoscolecid sclerites, may represent a deeper link connecting it with cycloneuralian outgroups.<ref name="Budd2001" /> Lobopodians are paraphyletic, and include the last common ancestor of arthropods, onychophorans and tardigrades.<ref name=":0"/>
Stem-group arthropods
Compared to other panarthropod stem-groups, suggestion on the lobopodian members of arthropod stem-group is relatively consistent — siberiid like Megadictyon and Jianshanopodia occupied the basalmost position, gilled lobopodians Pambdelurion and Kerygmachela branch next, and finally lead to a clade compose of Opabinia, Radiodonta and Euarthropoda (crown-group arthropods).<ref name="ReferenceA" /><ref name=":8" /><ref name=":2" /><ref name=":17" /><ref name=":10" /><ref name=":6" /><ref name=":11" />Template:Excessive citations inline Their positions within arthropod stem-group are indicated by numerous arthropod groundplans and intermediate forms (e.g. arthropod-like digestive glands, radiodont-like frontal appendages and dorso-ventral appendicular structures link to arthropod biramous appendages).<ref name=":8" /><ref name=":10" /> Lobopodian ancestry of arthropods also reinforced by genomic studies on extant taxa — gene expression support the homology between arthropod appendages and onychophoran lobopods, suggests that modern less-segmented arthropodized appendages evolved from annulated lobopodous limbs.<ref name=":21" /> On the other hand, primary antennae and frontal appendages of lobopodians and dinocaridids may be homologous to the labrum/hypostome complex of euarthropods, an idea support by their protocerebral origin<ref name=":8" /><ref name=":10" /><ref name=":14" /> and developmental pattern of the labrum of extant arthropods.<ref name=":21" /><ref name=":10" />
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Radiodonts are stem-group arthropods with gilled lobopodian-like body flaps, arthropodized frontal appendages and stalked compound eyes.
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Restoration of Pambdelurion a "gilled lobopodian" related to arthropods, which has both pairs of lobopods and lateral flaps.
Diania, a genus of armoured lobopodian with stout and spiny legs, were originally thought to be associated within the arthropod stem-group based on its apparently arthropod-like (arthropodized) trunk appendages.<ref name=":24" /> However, this interpretation is questionable as the data provided by the original description are not consistent with the suspected phylogenic relationships.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> Further re-examination even revealed that the suspected arthropodization on the legs of Diania was a misinterpretation — although the spine may have hardened, the remaining cuticle of Diania's legs were soft (not harden nor scleritzed), lacking any evidence of pivot joint and arthrodial membrane, suggest the legs are lobopods with only widely spaced annulations.<ref name=":12" /><ref name=":13" /> Thus, the re-examination eventually reject the evidence of arthropodization (sclerotization, segmentation and articulation) on the appendages as well as the fundamental relationship between Diania and arthropods.<ref name=":12" /><ref name=":13" />
Stem-group onychophorans
While Antennacanthopodia is widely accepted as a stem-group onychophoran,<ref name="ReferenceA" /><ref name=":2" /><ref name=":34" /><ref name=":6" /><ref name=":11" /><ref name=":27" /> the position of other xenusiid genera that were previously thought to be onychophoran-related is controversial — in further studies, most of them were either suggested to be stem-group onychophorans<ref name="ReferenceA" /><ref name=":2" /><ref name=":34" /><ref name=":27" /> or basal panarthropods,<ref name=":6" /><ref name=":11">Template:Cite journal</ref><ref name=":28" /> with a few species (Aysheaia<ref name=":6" /><ref name=":11" /><ref name=":28" />Template:Excessive citations inline or Onychodictyon ferox<ref name="ReferenceA" /><ref name=":2" />) occasionally suggested to be stem-group tardigrades. A study in 2014 suggested that Hallucigenia are stem-group onychophorans based on their claws, which have overlapped internal structures resembling those of an extant onychophoran.<ref name="ReferenceA" /> This interpretation was questioned by later studies, as the structures may be a panarthropod plesiomorphy.<ref name=":11" /><ref name=":28" />
Stem-group tardigrades
Lobopodian taxa of the tardigrade stem-group is unclear.<ref name=":0" /> Aysheaia<ref name=":6" /><ref name=":11" /><ref name=":28" /> or Onychodictyon ferox<ref name="ReferenceA" /><ref name=":2" /> had been suggest to be a possible member, based on the high claw number (in Aysheaia) and/or terminal lobopods with anterior-facing claws (in both taxa).<ref name="ReferenceA" /> Although not widely accepted, there are even suggestions that Tardigrada itself representing the basalmost panarthropod or branch between the arthropod stem-group.<ref name=":25" /> However, a paper in 2023 found luolishaniids to be the closest relatives of tardigrades using various morphological characteristics.<ref name="Kihm2023">Template:Cite journal</ref>
Stem-group panarthropods
It is unclear which lobopodians represent members of the panarthropod stem-group, and which were branched just before the last common ancestor of extant panarthropod phyla. Aysheaia may have occupied this position based on its apparently basic morphology;<ref name="Budd2001" /><ref name="ReferenceA" /><ref name=":2" /><ref name=":27" /> while other studies rather suggest luolishaniid and hallucigenid,<ref name=":6" /><ref name=":11"/><ref name=":28" /> two lobopodian taxa which had been resolved as members of stem-group onychophorans as well.<ref name=":0" /><ref name="ReferenceA" /><ref name=":2" /><ref name=":34" /><ref name=":27" />
Described genera
As of 2018, over 20 lobopodian genera have been described.<ref name=":13" /> The fossil materials being described as lobopodians Mureropodia apae and Aysheaia prolata are considered to be disarticulated frontal appendages of the radiodonts Caryosyntrips and Stanleycaris, respectively.<ref>Template:Cite journal</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Miraluolishania was suggested to be synonym of Luolishania by some studies.<ref name=":4" /><ref>Template:Cite journal</ref><ref name=":27" /> The enigmatic Facivermis was later revealed to be a highly specialized genus of luolishaniid lobopodians.<ref name=":9" /><ref name=":6" /><ref name=":27">Template:Cite journal</ref> Palaeocampa, formerly thought to be a fireworm, was also found as a lobopodian.<ref name=Knecht2025/>
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Fossil of Aysheaia pedunculata.
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Fossil of Microdictyon sinicum.
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Fossil of "Mureropodia apae", which may be in fact frontal appendage of Caryosyntrips cf. camurus.
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Reconstruction of Facivermis, an unusual lobopodian with limbless posterior region that lived like a tube worm
| Genus | Species | Family | Notes | Age | Location | Image |
|---|---|---|---|---|---|---|
| Paucipodia |
|
Paucipodiidae | An unarmoured lobopodian from the Chengjiang Biota. Probably a scavenger, it is equipped with paired claws at the end of each lobopod. Some are preserved alongside symbiotic epibionts. | Cambrian Stage 3 | Template:Flag | File:20210829 Paucipodia inermis diagrammatic reconstruction.png |
| Lenisambulatrix |
|
(Unassigned) | An unarmoured lobopodian with highly elongate, clawless lobopod limbs. | Cambrian Stage 3 | Template:Flag | File:20210928 Lenisambulatrix humboldti diagrammatic reconstruction.png |
| Diania |
|
(Unassigned) | A long-legged lobopodian covered entirely with weakly sclerotized spines and papillae. | Cambrian Stage 3 | Template:Flag | File:20210429 Diania cactiformis diagrammatic reconstruction.png |
| Cardiodictyon |
|
Cardiodictyidae | Lobopodian with extremely elongate body, with roughly 25 pairs of lobopod limbs, each associated with a saddle-shaped trunk sclerite. | Cambrian Stage 3 | Template:Flag | File:20210926 Cardiodictyon catenulum diagrammatic reconstruction.png |
| Xenusion |
|
Xenusiidae | Originally discovered around the time of the first World War, this lobopodian is known from glacial erratics from the early Cambrian. | Cambrian Stage 2 | Template:Flag | File:Xenusion auerswaldae 2.png |
| Onychodictyon |
|
Onychodictyidae | The body of this lobopodian was covered in numerous elongate papillae, each trunk segment bearing a pair of netted sclerites ending in a pointed tip. O. spiniferum (=Onychomicrodictyon spiniferum) is known from Greenland, it is considered by some to be a junior synonym. | Cambrian Stage 3 | Template:Flag Template:Flag Template:Flag | File:20210822 Onychodictyon ferox diagrammatic reconstruction.png |
| Orstenotubulus |
|
(unassigned) | Known from microscopic, three-dimensionally preserved Orsten-type fossils, which show the detailed ornament of the cuticle, and retractable spines that protrude from the inner surface of the limbs. | Guzhangian | Template:Flag | File:Orstenotubulus.png |
| Microdictyon |
|
Eoconchariidae | Globally distributed lobopodian, with most species known only from isolated sclerite plates, with are circular and net-like. Complete, soft-bodied fossils are found in the Chengjiang Biota, and the Kaili Biota. | Cambrian Stage 3 to Middle Cambrian | Template:Flag Template:Flag Template:Flag Template:Flag Template:Flag Template:Flag Template:Flag Template:Flag Template:Flag Template:Flag Template:Flag Template:Flag Template:Flag | File:20210915 Microdictyon sinicum diagrammatic reconstruction.png |
| Quadratapora |
|
Eoconchariidae | Eoconchariid lobopodian similar to Microdictyon. Known only from isolated plates. | Cambrian Stage 3 | Template:Flag Template:Flag | |
| Fusuchoncharium |
|
Eoconchariidae | Eoconchariid lobopodian similar to Microdictyon. Known only from isolated plates. | Cambrian Stage 3 | Template:Flag | |
| Hallucigenia |
|
Hallucigeniidae | One of the most famous fossil lobopodians, originally described from the Burgess Shale. Two other species have been described, but their placement within the genus remains uncertain. | Cambrian Stage 3 to Wuliuan | Template:Flag Template:Flag | File:20210000 Hallucigenia diagrammatic reconstruction.png |
| Rhombocorniculum |
|
Hallucigeniidae (Strictocorniculacea) | Only recently recognized as a lobopodian, this genus is known exclusively from isolated sclerites found around the world. The spines are flattened and twisting. | Cambrian Stage 3 | Template:Flag Template:Flag Template:Flag Template:Flag Template:Flag Template:Flag Template:Flag | |
| Strictocorniculum |
|
Hallucigeniidae (Strictocorniculacea) | Recognized as a lobopodian sclerite in 2025, this species is known from deep-water Cambrian deposits in Nova Scotia, and is allied with Rhombocorniculum by its tightly organized rhomboidal scales. | Cambrian Stage 2 to Cambrian Stage 3 | Template:Flag | |
| Carbotubulus |
|
Hallucigeniidae | The first marine lobopodian known from the Carboniferous, with three sets of differentiated legs, allying it with the hallucigeniids. | Moscovian | Template:Flag | |
| Thanahita |
|
Hallucigeniidae? | The only currently named Silurian lobopodian. Trunk was covered with numerous large tufted papillae, which follow a complex distribution. | Wenlockian | Template:Flag | File:Thanahita.jpg |
| Tritonychus |
|
Onychophora stem group? | A three-dimensionally preserved Orsten-type fossil from the Chengjiang Biota. | Cambrian Stage 3 | Template:Flag | |
| Luolishania |
|
Luolishaniida | Considered synonymous with Miraluolishania haikouensis. | Cambrian Stage 3 | Template:Flag | File:20210902 Luolishania longicruris Miraluolishania haikouensis diagrammatic reconstruction.png |
| Ovatiovermis |
|
Luolishaniida | An unarmoured luolishaniid lobopodian from the Burgess Shale, with anchoring lobopods bearing large claws at its posterior, and filter-feeding lobopods anteriorly. | Wuliuan–Drumian | Template:Flag | File:20210928 Ovatiovermis cribratus diagrammatic reconstruction.png |
| Facivermis |
|
Luolishaniida | A highly derived lobopodian which lacks any walking-lobopodians, bearing only 5 pairs of filter-feeding appendages anteriorly, with a long trunk terminating in a bulbous anchoring segment. Lived in constructed tubes buried in sediment, opening up to the water column. | Cambrian Stage 3 | Template:Flag | File:20210901 Facivermis yunnanicus diagrammatic reconstruction.png |
| Entothyreos |
|
Luolishaniida (Collinsovermidae) | A collinsovermid lobopodian with internal sclerite plates which acted similarly to arthropod tergites or vertebrae, reinforcing the body and allowing body erection for filter feeding. | Wuliuan–Drumian | Template:Flag | File:Entothryeos.png |
| Collinsovermis |
|
Luolishaniida (Collinsovermidae) | Known since 1983, this stout, highly armoured lobopodian (nicknamed "the Collins monster" after Desmond Collins, later lending this name to any collinsovermid lobopodian) did not receive a description until 2020. | Wuliuan–Drumian | Template:Flag | File:20210918 Collinsovermis monstruosus diagrammatic reconstruction.png |
| Collinsium |
|
Luolishaniida (Collinsovermidae) | Collinsovermid lobopodian with an elongate body bearing 15 pairs of lobopod limbs and sclerite spine sets. | Cambrian Stage 3 | Template:Flag | File:Collinsium reconstruction.jpg |
| Acinocricus |
|
Luolishaniida (Collinsovermidae) | Highly armoured collinsovermid lobopodian with hundreds of spines borne on whorls, set between the limbs rather than above them. | Wuliuan | Template:Flag | File:Acinocricus stichus.png |
| Beorn |
|
Crown-group Tardigrada (Eutardigrada) | The first fossil tardigrade ever discovered, found in a sample of Cretaceous amber from Cedar Lake, Manitoba. Named after a character from The Hobbit. | Campanian | Template:Flag | File:Beorne (holotype, MCZ PALE-5213).png |
| Aerobius |
|
Crown-group Tardigrada (Eutardigrada) | A fossil tardigrade found in the same amber sample as Beorn leggi, which was formally described using modern imaging techniques in 2024. | Campanian | Template:Flag | File:Beorn and Aerobius (life reconstruction).png |
| Paradoryphoribius |
|
Crown-group Tardigrada (Eutardigrada) | The third fossil tardigrade to be named, found in an amber sample which also contained three ants, a beetle, and a flower. | Burdigalian | Template:Flag | File:Fossil Tardigrade Dominican Amber.png |
| Milnesium |
|
Crown-group Tardigrada (Eutardigrada) | A Cretaceous species of Milnesium, a large, common genus of extant tardigrade. | Turonian | Template:Flag | |
| Aysheaia |
|
Aysheaiidae | Originally described as an annelid, entomologists quickly pointed out similarities between this Burgess Shale fossil and living velvet worms. | Wuliuan–Drumian | Template:Flag | File:20210904 Aysheaia pedunculata diagrammatic reconstruction.png |
| Hadranax |
|
Aysheaiidae | Known from only 3 specimens, this lobopodian was large, short-legged, and possessed incredibly elongate frontal appendages. It is found in the deep-sea deposits of Sirius Passet. | Wuliuan–Drumian | Template:Flag | File:20220306 Hadranax augustus diagrammatic reconstruction.png |
| Palaeocampa |
|
Aysheaiidae | Only known freshwater lobopodian. Originally described as a caterpillar, and later a polychaete, it was redescribed in 2025 as a lobopodian with venomous spines. | Moscovian to Stephanian | Template:Flag Template:Flag | File:Palaeocampa anthrax reconstruction1.jpg |
| Antennacanthopodia |
|
Stem-Onychophora? | A rare lobopodian from the Chengjiang Biota, notable for its resemblance to modern onychophorans. As it was a marine species, the second pair of head appendages could not have functioned like the slime papillae of velvet worms. | Cambrian Stage 3 | Template:Flag | File:20210829 Antennacanthopodia gracilis diagrammatic reconstruction.png |
| Helenodora |
|
Onychophora | A putative velvet worm from Mazon Creek, whether or not it lived on land or in the ocean is debated. | Moscovian | Template:Flag | File:Helenodora.jpg |
| Antennipatus |
|
Onychophora | A velvet worm from Montceau-les-Mines. | Stephanian | Template:Flag | |
| Cretoperipatus |
|
Crown-group Onychophora | A Cretaceous-age velvet worm from Burmese amber, this velvet worm lived alongside dinosaurs in a tropical forest environment. | Cenomanian | Template:Flag | File:Cretoperipatus.jpg |
| Succinipatopsis |
|
Crown-group Onychophora? | Known from a single fossil preserving the posterior half of a velvet worm, although this conclusion is debated. | Eocene | Template:Flag? | |
| Tertiapatus |
|
Onychophora? | A single fossil originally described as a velvet worm, although some authors consider it to be arthropodized, and thus likely not a velvet worm. | Eocene–Miocene | Template:Flag | |
| Siberion |
|
Siberiidae | Known from only two fossils, the fossil site this species come from has since been destroyed. | Early Cambrian | Template:Flag | File:20191215 Siberion lenaicus.png |
| Megadictyon |
|
Siberiidae | A siberiid lobopodian with a body up to 20 centimetres long, which remains poorly described. | Cambrian Stage 3 | Template:Flag | File:20191118 Megadictyon cf. haikouensis.png |
| Jianshanopodia |
|
Siberiidae | A siberiid lobopodian with a body up to 30 centimetres long. The trunk lobopods are lined with tree-like branching papillae on their posterior edge, probably a respiratory feature. | Cambrian Stage 3 | Template:Flag | File:20210914 Jianshanopodia decora diagrammatic reconstruction.png |
| Kerygmachela |
|
Kerygmachelidae | A pelagic lobopodian from the Sirius Passet. It had a trunk lined with sets of small, sclerotized nodes, to which muscles attached. | Cambrian Stage 3 | Template:Flag | File:20191022 Kerygmachela kierkegaardi without lobopods.png |
| Mobulavermis |
|
Kerygmachelidae | A large pelagic kerygmachelid lobopodian with a high number of body flap pairs, known from two specimens from the Pioche Shale. | Cambrian Stage 4 | Template:Flag | File:20231214 Mobulavermis adustus diagrammatic reconstruction.png |
| Utahnax |
|
Kerygmachelidae | A large pelagic lobopodian, probably related to Kerygmachela. Its lobopodous appendages are flattened as to form flaps. | Drumian | Template:Flag | File:20231215 Utahnax vannieri diagrammatic reconstruction.png |
| Pambdelurion |
|
(Unassigned) | A large, 50 centimetre long lobopodian from Sirius Passet. Possessing both legs and flaps (the latter of which apparently lack musculature), this was the apex predator of the ecosystem. | Cambrian Stage 3 | Template:Flag | File:20191112 Pambdelurion whittingtoni.png |
| Omnidens |
|
(Unassigned) | The largest known Cambrian animal, reaching an estimated ~1.7 metres in length, based on the closely related Pambdelurion. Known from large sclerotized jaws and the terminal, sclerotized talons of the frontal appendages. | Cambrian Stage 3 | Template:Flag | File:Omnidens reconstruction.jpg |
| Opabinia |
|
Opabiniidae | A "weird wonder" of the Cambrian with frontal appendages adapted into an elongate proboscis, and 5 eyes on the head. | Wuliuan–Drumian | Template:Flag | File:20191108 Opabinia regalis.png |
| Utaurora |
|
Opabiniidae | The first new opabiniid described since 1912, this species is known from a single specimen from the Wheeler Shale of Utah. | Drumian | Template:Flag | File:20220212 Utaurora comosa.png |
| Mieridduryn |
|
Opabiniidae | A probably opabiniid from the Ordovician of Wales, found at the Castle Bank Lagerstätte. This species apparently lacks eyes, with its head covered instead by a small cephalic sclerite, but does possess both flaps and lobopods, and a frontal proboscis. | Middle Ordovician | Template:Flag | File:20221119 Mieridduryn bonniae diagrammatic reconstruction.png |
| Youti? |
|
(Unassigned) | An embryonic panarthropod from the Yu'anshan Formation, preserved three-dimensionally in Orsten-style, this fossil provides a remarkable view into the internal anatomy of early panarthropods. | Cambrian Stage 3 | Template:Flag | File:Youti yuanshi.jpg |
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