The importance of Panarthropoda in today's society is undeniable. Whether it is a current topic or a historical event, Panarthropoda plays a vital role in people's lives. Over the years, Panarthropoda has been the subject of debate, analysis and reflection in different areas, from politics and economics to culture and entertainment. In this article, we will explore the impact of Panarthropoda on everyday life, as well as its influence on decision-making and human behavior. From its importance in the workplace to its influence on mental and emotional health, Panarthropoda has a reach that transcends borders and time.
Panarthropoda is a proposed animalclade containing the extant phylaArthropoda, Tardigrada (water bears) and Onychophora (velvet worms).Panarthropods also include extinctmarine 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. However the term "Lobopodia" is sometimes expanded to include tardigrades and onychophorans as well.
Not all studies support the monophyly of Panarthropoda, but most do, including neuroanatomical,phylogenomic and palaeontological studies. At least a close relationship between onychophorans and arthropods is widely agreed upon, but the position of tardigrades is more controversial. Some phylogenomic studies have found tardigrades to be more closely related to nematodes. 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. While annelids are placed among the Spiralia (making them more closely related to mollusks, flatworms and such), having evolved their segmented bodies convergently.
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).
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 (Lobopodiasensu Smith & Goldstein 2017).
Tactopoda had been supported by mitochondrial gene arrangements, palaeontological and neuroanatomical evidences, specifically the presence of segmented ganglia shared by arthropods and tardigrades. 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. 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. 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, while the others mostly recovering either Antennopoda or Onychophora+Tardigrada.
Anatomy of onychophoran anterior region, showing specialized appendages (ant, md) and deutocerebrum (D).
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.
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