Palæos:		Arthropoda
INVERTEBRATES		Panarthropoda

Parent: Ecdysozoa	Sister: Lophotrochozoa?	Arthropoda
Child: Chaetognatha	Child: Arthropoda	Invertebrates

 

Panarthropoda

Arthropods and their relatives

Arthropoda Home Introduction Phylogeny References

Arthropoda Arthropod Phylogeny Panarthropoda Lobopoda Anomalocarida basal Arthropods Arachnomorpha Trilobita Chelicerata Crustacea Myriapoda Hexapoda

Panarthropods include true arthropods and their soft-bodied relatives, the tardigrades and onychophorans. These share a number of unique features (apomorphies), such as "cuticle of a-chitin which is molted regularly, appendages with chitinous claws, and mixocoel with metanephridia and ostiate heart (absent in tardigrades); several characters, such as the structure of the brain, indicate that arthropods and tardigrades are sister groups." Nielsen, "The Phylogenetic position of the Arthropoda"

During the Cambrian period, Panarthropods were much more diverse than today. There were several different lineages of lobopods and proto-arthropods, including large carnivorous swimming forms like Anomalocaris and Kerygmachela, as well as smaller crawling types.

Whilst true arthropods, tardigrades and onychophorans are highly differentiated in form today, such was not always the case. During Cambrian Epoch 2, many transitional forms co-existed, and exciting new discoveries have come to light. Of particular interest is the afore-mentioned Kerygmachela, which provides a link between the lobopods, anomalocarids and arthropods. Another new anomalocarid-like taxon, Pambdelurion , indicates that the biramous arthropods actually arose from within the anomalocaridids. Budd, "Stem-group arthropods from the Lower Cambrian Sirius Passet fauna of North Greenland

After dominating the oceans for many millions of years, the big protoarthropods died out with the end-Cambrian extinction, their place as super-predators being taken by cephalopod mollusks during the Ordovician.

Phylogeny of Crown-Arthropoda after Conway Morris and Hou & Bergström

<==o ARTHROPODA  [polyphyletic??]
   |?-+?- TARDIGRADA (water bears) [are Aschelmithes?? (Hou & Bergström, 1997)]
   |  `--+-- LOBOPODA [Onychophora sensu lato]PROGONEATA (lobopods, velvet worms)
   |     `-- UNIRAMIA (uniramous arthropods, i.e. myriapods & insects)
   `--+--o †"ANOMALOCARIA "
      |  |?- †Kerygmachela kierkegaardi
      |  |--o †OPABINIDA
      |  |  `-- †Opabinia
      |  `--o †ANOMALOCARIDA
      |     |== †other anomalocarids
      |     `-- †Anomalocaris
      `-- SCHIZORAMIA (crustaceans & chelicerates)

Links

Links

Akam, M. 2000. Arthropods: Developmental diversity within a (super) phylum. PNAS 97(9): 4438-41. - Hox genes and Arthropod evolution and morphology

Arthropoda (Tree of Life)

The colonization of land by animals: molecular phylogeny and divergence times among arthropods

Late Precambrian bilaterians: grades and clades