Ecdysozoa

From Palaeos

Choanomonada
`--Metazoa
   `==Porifera (paraphyletic?)
      `==Radiata (paraphyletic?)
         `--Bilateria
            `==Acoelomorpha (paraphyletic?)
               |--Protostomia
               |  |--Ecdysozoa
               |  `--Lophotrochozoa
               `--Deuterostomia

(Arthropoda, Diplopoda, Polydesmida, Eurydesmidae)

The Ecdysozoa, for our purposes, are trated as bugs > slugs -- a stem group leading to the Arthropoda. However, they are better known as the "molting clade" -- the animal phyla with a cuticle which is molted (ecdysis. There is still considerable suspicion that they might not be a clade. However, the validity of the Ecdysozoa is coming increasingly to be accepted among workers in this field.

Phyla included are the Arthropoda, Tardigrada, Onychophora, and probably also the more primitive worm-like and "pseudocoelomate" groups like the Nematoda, Nematomorpha, Priapula, Kinorhyncha and Loricifera.

The largest of these phyla, and the most speciose phylum in the animal kingdom, the Arthropoda, includes insects, spiders, crabs, and their kin. All these organisms have a body divided into repeating segments, typically with paired appendages. Two smaller phyla, the Onychophora and Tardigrada, are close relatives of the arthropods and share these traits. These ogether make up the "Panarthropoda".

The Nematoda or roundworms, the second largest animal phylum. Roundworms are typically microscopic, and occur in nearly every environment where there is water. A number are important parasites. Smaller phyla related to them are the Nematomorpha or horsehair worms, which are invisible to the unaided eye, and the Kinorhyncha, Priapulida, and Loricifera. These groups have a reduced coelom, called a pseudocoelom.

Protostomia
`--Ecdysozoa
   |--Scalidophora
   |?--Protoconodonta†
   |   `--Chaetognatha
   |--+--Nematomorpha
   |  `--Nematoda
   `--o--Lobopoda 
      `--+--Tardigrada
         `--+--Anomalocarida
            `--Arthropoda

[edit] Phylogeny

<==Ecdysozoa [Nematozoa]
   |--Introverta
   |    |  i. s.: Myxozoa
   |    |--+--+--Ancalagon
   |    |  |  `--Fieldia
   |    |  `--+--Scalidophora
   |    |     `--Markuelia Val’kov 1983
   |    |          |--*M. secunda
   |    |          `--M. hunanensis Dong, Donoghue et al. 2004
   |    `--+--Chaetognatha
   |       `--Nematoida [Nematoidea]
   |            |--Nematoda
   |            `--Nematomorpha
   `--Panarthropoda [Dicephalosomata, Haemopoda, Mandibulopoda, Uniantennata, Uniramia]
        |--Lobopoda
        |    |  i. s.: Microdictyon sinicum
        |    |--Tardigrada
        |    `--+--Xenusion
        |       `--+--Hallucigenia sparsa [=Canadia sparsa]
        |          `--+--Onychophora
        |             `--Aysheaia Walcott 1911
        |                  `--A. pedunculata
        `--+--+--Parapeytoia
           |  `--Arthropoda
           `--+--Probosciferidea [Opabiniida, Opabiniidacea]
              |    |--Kerygmachela Conway Morris et al. 1987
              |    |    `--K. kierkegaardi
              |    `--+--Opabinia Walcott 1912
              |       |    `--O. regalis
              |       `--Tullimonstrum Richardson 1966 [Tullimonstrida, Tullimonstridea]
              |            `--T. gregarium
              `--Anomalocaridea
                   |--Cassubia Lendzion 1977 [Cassubiata]
                   |    `--C. infracambriensis
                   `--Anomalocarida [Anomalocaridata]
                        |--Hurdia Walcott 1912
                        `--Anomalocaris Whiteaves 1892 (see below for synonymy)
                             |--*A. canadensis Whiteaves 1892
                             `--A. nathorsti (Walcott 1911) (see below for synonymy)

Anomalocaris Whiteaves 1892 [incl. Laggania Walcott 1911, Peytoia Walcott 1911]

Anomalocaris nathorsti (Walcott 1911) [=*Peytoia nathorsti; incl. *Laggania cambria Walcott 1911]

* Type species of genus indicated

[edit] References

Bousfield, E. L. 1995. A contribution to the natural classification of Lower and Middle Cambrian arthropods: Food-gathering and feeding mechanisms. Amphipacifica 2: 3-34.

Budd, G. E. 2002. A palaeontological solution to the arthropod head problem. Nature 417: 271-275.

Cavalier-Smith, T. 1998. A revised six-kingdom system of life. Biological Reviews 73: 203-266.

Conway Morris, S. 1998. The Crucible of Creation. Oxford University Press: Oxford.

Dong, X-P., P. C. J. Donoghue, H. Cheng & J.-B. Liu. 2004. Fossil embryos from the Middle and Late Cambrian period of Hunan, south China. Nature 427: 237-240.

Giribet, G. 2002. Current advances in the phylogenetic reconstruction of metazoan evolution. A new paradigm for the Cambrian explosion? Molecular Phylogenetics and Evolution 24: 345-357.

Giribet, G., D. L. Distel, M. Polz, W. Sterrer & W. C. Wheeler. 2000. Triploblastic relationships with emphasis on the acoelomates and the position of Gnathostomulida, Cycliophora, Plathelminthes, and Chaetognatha: A combined approach of 18S rDNA sequences and morphology. Systematic Biology 49: 539-562.

Giribet, G., G. D. Edgecombe & W. C. Wheeler. 2001. Arthropod phylogeny based on eight molecular loci and morphology. Nature 413: 157-161.

Giribet, G., & C. Ribera. 1998. The position of arthropods in the animal kingdom: A search for a reliable outgroup for internal arthropod phylogeny. Molecular Phylogenetics and Evolution 9: 481-488.

Okamura, B., A. Curry, T. S. Wood & E. U. Canning. 2002. Ultrastructure of Buddenbrockia identifies it as a myxozoan and verifies the bilaterian origin of the Myxozoa. Parasitology 124: 215-223.

Schmidt-Rhaesa, A. 2002. Are the genera of Nematomorpha monophyletic taxa? Zoologica Scripta 31 (2): 185-200.

Wharton, D. A., R. Poulin & C. L. Tyrell. 2001. Parasites of anostostomatid insects. In The Biology of Wetas, King Crickets and Their Allies (L. H. Field, ed.) pp. 259-267. CABI Publishing: Wallingford (UK).

Whittington, H. B., & D. E. G. Briggs. 1985. The largest Cambrian animal, Anomalocaris, Burgess Shale, British Columbia. Philosophical Transactions of the Royal Society of London 309: 569-609.

Zrzavý, J., V. Hypša & D. F. Tietz. 2001. Myzostomida are not annelids: Molecular and morphological support for a clade of animals with anterior sperm flagella. Cladistics 17: 170-198.

[edit] Credits

Palaeos com MAK020407 ATW050806; Wikipedia, this page MAK061012, phylogeny CKT070909