Palaeos		Ecdysozoa
Metazoa		Classification

Ecdysozoa: Classification

BILATERIA
|--DEUTEROSTOMIA
`--Protostomia 
   |--SPIRALIA
   |
   `----ECDYSOZOA = paraphyletic Scalidophora?
      |==Palaeoscolecida
      |==Priapozoa
      |  |--Kinorhyncha
      |  `--+--Priapulida
      |     `-- Loricifera
      `--+--Nematoida
         |   |--Nematoda
         |    `--Nematomorpha
         `--Panarthropoda
            |--Tardigrada
            `--+--Onychophora
                `--+--Dinocaridida
                   `--ARTHROPODA

As Ecdysozoa is a molecular phylogenetic and cladistic concept (see dendrogram page), there is little in the way of Linnaean-evolutionary based systematics. One of the few systematists still using a rank-based and paraphyletic/evolutionary (ancestral taxa) classification system is Thomas Cavalier-Smith, the Canadian microbiologist who has created a comprehensive revised classification of the kingdoms of life on Earth (Cavalier-Smith (1998)). He presents the Ecdysozoa as folows (our comments in square brackets):

Infrakingdom 3. Ecdysozoa
  Superphylum 1. Haemopoda [= Panarthropoda]
    Phylum 1. Arthropoda
      Subphylum 1. Cheliceromorpha
        Infraphylum 1. Pycnogonida
        Infraphylum 2. Chelicerata
      Subphylum 2. Trilobitomorpha
      Subphylum 3. Mandibulata
        Infraphylum 1. Crustacea
        Infraphylum 2. Myriapoda
        Infraphylum 3. Insecta [ = Hexapoda]
    Phylum 2. Lobopoda [= Lobopodia]
      Subphylum 1. Onychophora
      Subphylum 2. Tardigrada
  Superphylum 2. Nemathelminthes [= Cycloneuralia]
    Phylum Nemathelminthes
      Subphylum 1. Scalidorhyncha [= Scalidophora]
        Infraphylum 1. Priapozoa (classes Priapula, Loricifera).
        Infraphylum 2. Kinorhyncha
      Subphylum 2. Nematoida
        Infraphylum 1. Nematoda
        Infraphylum 2. Nematomorpha

Whereas the standard consensus has around 38 animal phyla (including 8 in Ecdysozoa alone), Cavalier-Smith is concerned to reduce the excessive number of phyla that he considers are the result of taxonomic inflation. Hence he has has only 23 phyla, of which only three belong to the Ecdysozoa. While agreeing with the need to reduce the number of high rank taxa, we would not be quite so radical. The following classification is based mostly on Cavalier-Smith's, with some terminological adjustment to bring it line with our current coverage. Because there are only five phyla here, we have removed intermediate ranks such as Scalidophora (= Cephalorhyncha = Nemathelminthes = Scalidorhyncha) and Panarthropoda Nielsen, 1995 (= Haemopoda Cavalier-Smith 1998 = Aiolopoda Hou and Bergström, 2006);, thus allowing Protostomia to retain infrakingdom status and avoiding the need for additional high level ranks like "branch" (between sub and infrakingdom, or infrakingdom and phylum) . In keeping with the evolutionary-linnaean arrangement, this includes a large number of paraphyletic grades MAK120425

Kingdom Animalia (cont.)
  Subkingdom Bilateria (cont.)
  Infrakingdom Protostomia (cont.)
    Superphylum Ecdysozoa Aguinaldo et al. 1997 (moulting animals; Camb - Rec)
      incertae sedis
              (Markuelia, Camb)
      Phylum Priapozoa Cavalier-Smith 1998 (larva or adult with cuticular lorica; Camb-Rec).
        Subphylum Priapula (Priapozoa sensu stricta)
            Class undertermined - various Cambrian forms
            Class Palaeoscolecida (armour-plated priapozoans Camb-Sil)
            Class Priapulida (Penis worms, Camb or Carb to Rec)
        Subphylum Loricifera (tiny or microscopic, with lorica Camb-Rec)
      Phylum Kinorhyncha Reinhard 1887 (tiny or microscopic, segmented; without lorica - no fossil record).
      Phylum Nematoida Rudolphi 1808 (primitively parasitic worms, many free-living and microscopic, v poor fossil record)
        Subphylum Nematoda Gegenbaur 1859 (Roundworms - Carb to Rec)
        Subphylum Nematomorpha Vejovsky 1886 (Horsehair worms, - no fossil record).
      Phylum Lobopodia Snodgrass, 1938 (= Protarthropoda Lankester, 1904 = Lobopoda Cavalier-Smith 1998 ; soft cuticle; unjointed limbs with terminal claws ; both muscles and hydraulic pressure involved in locomotion; evolutionary grade, Camb-Rec).
        Subphylum Tardigrada Doyère 1840 (water bears, e.g. Echiniscus. Microscopic.Camb-Rec).
        Subphylum Onychophora Grube 1853 (velvet worms, e.g. Peripatus, Cambrian? or Carb to Rec)
              Class Xenusia Dzik & Krumbiegel, 1989 (Paleozoic lobopods, traditionally included under Onychophora - paraphyletic/ancestral panarthropod grade - Camb-Sil)
              Class Euonychophora Hutchinson, 1930 (terrestrial onychophora, crown and some stem group taxa - Carb-Rec)
        Subphylum "Protarthropoda" (used here as paraphyletic bridging taxon between lobopods and arthropods)
              Class Dinocaridida Collins, 1996 (paraphyletic grade of swimming and gilled lobopods, include Anomalocaridid superpredators Camb to Dev)
      Phylum Arthropoda von Siebold and Stannius 1848 (jointed exoskelton Camb-Rec).
        Subphyla unspecified
              Class Megacheira Hou and Bergström 1997 ("Geat Appendage" Arthropods - Camb)
              Class Marellamorpha - (monotypal for Marella and co, probably should be included under another higher rank taxon - Camb-Dev)
        Subphylum Arachnomorpha Størmer 1944
          Infraphylum Trilobitomorpha Størmer 1944 (trilobites and related forms - Camb - Perm).
          Infraphylum Cheliceromorpha Boudraux 1978
            Superclass Pycnogonida Latreille 1810 (sea spiders, e.g. Nymphon Camb-Rec).
            Superclass Chelicerata Heymons 1901 (Horseshoe crabs (Limulus and co), eurypterids, arachnids Camb-Rec).
        Subphylum Crustacea Pennant 1777 (e.g. copepods, ostracods, barnacles, crabs, shrimps, Cambrian to Rec).
        Subphylum Atelocerata (= Uniramia, unranched limbs, (monophyletic according to morphology of fossil & recent froms, polyphyletic according to molecular phylogeny)
            Superclass Myriapoda Leach 1814 (centipedes, millipedes, symphylans, pauropods; Sil to Rec).
            Superclass Hexapoda (insects and related primitive forms; Dev to Rec)