List of bilaterian orders

Bilateria is an extremely diverse group of animals containing a vast majority of its species, largely due to the enormous amount of arthropods. This article is a list of orders contained within Bilateria separated by phylum. Groups that are not contained within an order are listed separately.

The relative number of species contributed to the total by each phylum of animals. Arthropoda is the phylum with the most individual organisms.

List

Phylum Annelida

Hirudo medicinalis. Order Arhynchobdellida

Annelid taxonomy is currently under constant revisions due to the discovery that the class Polychaeta is paraphyletic. As such, a comprehensive list of orders is likely to change depending on what is accepted as valid.

• Amphinomida

Class Sipuncula

• Aspidosiphonida
• Golfingiida
• Phascolosomatida

Clade Pleistoannelida

• Clade Errantia
  • Eunicida
  • Phyllodocida
  • Protodrilida
• Myzostomida
• Clade Sedentaria
  • Capitellida^[a]
    • Family Capitellidae
    • Subclass Echiura
      • Bonelliida
      • Echiurida
  • Opheliida
  • Orbiniida
  • Sabellida
  • Spionida
  • Terebellida
  • Class Clitellata
    • Branchiobdellida
    • Haplotaxida
    • Lumbriculida
    • Moniligastrida
    • Subclass Hirudinea
      • Rhynchobdellida
      • Arhynchobdellida

Unplaced groups

• Genus Apistobranchus
• Suborder Chaetopteriformia
• Suborder Cirratuliformia
• Genus Lobatocerebrum
• Clade Maldanomorpha
• Clade Paleoannelida
• Family Polygordiidae
• Family Siboglinidae^[b]

Phylum Arthropoda

The house fly. Order Diptera

See List of arthropod orders

Phylum Brachiopoda

Terebratalia transversa. Order Terebratulida

Class Craniata

• Craniida
• Craniopsida †
• Trimerellida †

Subphylum Linguliformea

• Class Lingulata
  • Acrotretida †
  • Lingulida
  • Siphonotretida †
• Class Paterinata
  • Paterinida †

Subphylum Rhynchonelliformea

• Class Chileata
  • Chileida †
  • Dictyonellida †
• Class Kutorginata
  • Kutorginida †
• Class Obolellata
  • Naukatida †
  • Obolellida †
• Class Rhynchonellata
  • Athyridida †
  • Atrypida †
  • Orthida †
  • Protorthida †
  • Pentamerida †
  • Rhynchonellida
  • Spiriferida †
  • Terebratulida
  • Thecideida
• Class Strophomenata
  • Billingsellida †
  • Orthotetida †
  • Productida †
  • Strophomenida †

Phylum Bryozoa

A colony of Membranipora membranacea. Order Cheilostomatida

Class Gymnolaemata

• Cheilostomata
• Ctenostomatida

Class Phylactolaemata

• Plumatellida

Class Stenolaemata

• Cyclostomatida
• Cryptostomata †
• Cystoporida †
• Esthonioporata †
• Fenestrata †
• Timanodictyina^[c] †
• Trepostomatida †

Phylum Chaetognatha

Spadella cephaloptera. Order Phragmophora

• Aphragmophora
• Phragmophora
• Protoconodonta †

Unplaced groups

• Genus Capinatator
• Genus Eognathacantha
• Genus Protodagitta
• Genus Timorebestia

Phylum Chordata

The great white shark. Order Lamniformes

See List of chordate orders

Phylum Cycliophora

Symbion americanus. Order Symbiida

Class Eucycliophora

• Symbiida

Phylum Dicyemida

Dicyema japonicum

Dicyemida does not contain any established orders but does contain three families: Conocyemidae, Dicyemidae and Kantharellidae

Phylum Echinodermata

Asterias rubens. Order Forcipulatida

See List of echinoderm orders

Phylum Entoprocta

A colony of Barentsia ramosa

Entoprocta has no orders but is split into four families; Barentsiidae, Pedicellinidae, Loxokalypodidae, and Loxosomatidae

Phylum Gastrotricha

Paradasys subterraneus. Order Macrodasyida

• Chaetonotida
• Macrodasyida

Phylum Gnathostomulida

Gnathostomula paradoxa. Order Bursovaginoidea

• Bursovaginoidea
• Filospermoidea

Phylum Hemichordata

Unknown species of acorn worm (class Enteropneusta).

The classes Planctosphaeroidea and Enteropneusta do not contain any orders

Class Pterobranchia

• Cephalodiscida
• Subclass Graptolithina
  • Rhabdopleurida
  • Dendroidea †
  • Graptoloidea †

Unplaced groups

• Family Cysticamaridae
• Family Wimanicrustidae
• Family Dithecodendridae
• Family Cyclograptidae

Phylum Kinorhyncha

Echinoderes marthae. Order Echinorhagata

Class Cyclorhagida

• Echinorhagata
• Kentrorhagata
• Xenosomata

Class Allomalorhagida

• Anomoirhaga

Unplaced groups

• Genus Eokinorhynchus
• Family Pycnophyidae

Phylum Loricifera

Spinoloricus cinziae. Order Nanaloricida

Loricifera has no classes and all species are contained within one order

• Nanaloricida

Phylum Micrognathozoa

Limnognathia maerski. Order Limnognathida

Micrognathozoa has no classes and its single species is placed in one order

• Limnognathida

Phylum Mollusca

Sepioteuthis sepioidea. Order Myopsida

See List of mollusc orders

Phylum Nematoda

Caenorhabditis elegans. Order Rhabditida

Nematode taxonomy is far from fully resolved, and different schemes might be used. For this list, Mike Hodda's Phylum Nematoda: a classification, catalogue and index of valid genera, with a census of valid species classification is used.^[1]

Class Enoplea

• Subclass Enoplia
  • Superorder Enoplica
    • Alaimida
    • Enoplida
    • Ironida
    • Trefusiida
    • Tripyloidida
  • Superorder Rhaptothyreica
    • Rhaptothyreida
• Subclass Oncholaimia
  • Oncholaimida
• Subclass Triplonchia
  • Triplonchida
  • Tripylida

Class Dorylaimea

• Subclass Dorylaimia
  • Dorylaimida
• Subclass Bathyodontia
  • Bathyodontida
  • Mononchida
  • Mermithida
• Subclass Trichocephalia
  • Trichocephalida
  • Marimermithida
  • Dioctophymatida
  • Muspiceida

Class Chromadorea

• Subclass Chromadoria
  • Chromadorida
  • Selachinematida
  • Desmodorida
  • Desmoscolecida
• Subclass Plectia
  • Superorder Monhysterica
    • Monhysterida
  • Superorder Plectica
    • Leptolaimida
    • Plectida
    • Benthimermithida
  • Superorder Teratocephalica
    • Teratocephalida
  • Superorder Rhabditica
    • Diplogasterida
    • Rhabditida
    • Spirurida
    • Rhigonematida
    • Panagrolaimida
    • Drilonematida

Phylum Nematomorpha

Paragordius tricuspidatus. Order Gordioidea

• Gordioidea
• Nectonematoidea

Phylum Nemertea

Baseodiscus quinquelineatus. Order Heteronemertea

Class Hoplonemertea

• Monostilifera
• Polystilifera

Class Palaeonemertea

• Archinemertea
• Carinomiformes
• Tubulaniformes

Class Pilidiophora

• Heteronemertea

Phylum Onychophora

Epiperipatus biolleyi

Onychophora contains no classes and no orders, but is split into two living families; Peripatidae and Peripatopsidae, and 5 extinct genera; Antennacanthopodia, Antennipatus, Helenodora, Succinipatopsis, and Tertiapatus.

Phylum Orthonectida

A drawing of Rhopalura giardii

Orthonectida contains no classes or orders, but is split into two families; Pelmatosphaeridae and Rhopaluridae

Phylum Phoronida

Phoronopsis harmeri

Phoronida contains no classes, orders, or families, but is split into two genera; Phoronis and Phoronopsis

Phylum Platyhelminthes

Pseudoceros ferrugineus. Order Polycladida

The class Catenulida contains no orders.

Subphylum Rhabditophora

• Clade Macrostomorpha
  • Macrostomida
• Clade Trepaxonemata
  • Gnosonesimida
  • Clade Amplimatricata
    • Lecithoepitheliata
    • Polycladida
  • Clade Euneoophora
    • Proseriata
    • Rhabdocoela
    • Clade Acentrosomata
      • Clade Adiaphanida
        • Prolecithophora
        • Fecampiida
        • Tricladida
      • Clade Bothrioneodermata
        • Bothrioplanida
        • Superclass Neodermata
          • Class Cestoda
            • Subclass Cestodaria
              • Amphilinidea
              • Gyrocotylidea
            • Subclass Eucestoda
              • Spathebothriidea
              • Caryophyllidea
              • Haplobothriidea
              • Diphyllobothriidea
              • Diphyllidea
              • Trypanorhyncha
              • Bothriocephalidea
              • Litobothriidea
              • Lecanicephaloidea
              • Rhinebothriidea
              • Tetraphyllidea
              • Onchoproteocephalidea
              • Nippotaeniidea
              • Tetrabothriidea
              • Cyclophyllidea
          • Class Monogenea
            • Subclass Monopisthocotylea
              • Monocotylidea
              • Capsalidea
              • Lagarocotylidea
              • Montchadskyellidea
              • Gyrodactylidea
              • Dactylogyridea
            • Subclass Polyopisthocotylea
              • Polystomatidea
              • Chimaericolidea
              • Diclybothriidea
              • Mazocraeidea
          • Class Trematoda
            • Subclass Aspidogastrea
              • Aspidogastrida
              • Stichocotylida
            • Subclass Digenea
              • Diplostomida
              • Plagiorchiida

Unplaced groups

• Genus Haplopharynx

Phylum Priapulida

Priapulus caudatus. Order Priapulimorphida

Several stem group priapulid genera are not classified within any established orders. The orders listed below are solely crown priapulids.

• Halicryptomorphida
• Priapulimorphida
• Meiopriapulomorpha
• Seticoronaria^[d]

Phylum Rotifera

Habrotrocha rosa. Order Philodinida

The group Acanthocephala is traditionally treated as a separate phylum from Rotifera. However, it was found that Acanthocephala are phylogenetically contained within the rotifers, and this list reflects these findings.^{[citation needed]}

• Seisonida

Superclass Eurotatoria

• Class Bdelloidea
  • Adinetida
  • Philodinavida
  • Philodinida
• Class Monogononta
  • Collothecaceae
  • Flosculariaceae
  • Ploima

Clade Acanthocephala

• Class Archiacanthocephala
  • Apororhynchida
  • Gigantorhynchida
  • Moniliformida
  • Oligacanthorhynchida
• Class Eoacanthocephala
  • Gyracanthocephala
  • Neoechinorhynchida
• Class Palaeacanthocephala
  • Echinorhynchida
  • Heteramorphida
  • Polymorphida
• Polyacanthorhynchida

Phylum Tardigrada

Acutuncus antarcticus. Order Parachela

The class Mesotardigrada contains one species, Thermozodium esakii, which has not been found since its reported discovery in 1937, and its existence is dubious. It is contained within the order Thermozodia.

• Class Eutardigrada
  • Apochela
  • Parachela
• Class Heterotardigrada
  • Arthrotardigrada
  • Echiniscoidea

Phylum Xenacoelomorpha

Neochildia fusca. Order Acoela

The subphylum Xenoturbellida does not contain any classes or orders. Its only family is Xenoturbellidae which contains one genus, Xenoturbella.

• Subphylum Acoelomorpha
  • Acoela

The class Nemertodermatida does not contain any orders, but does contain two families; Ascopariidae and Nemertodermatidae.

Notes

1. This order traditionally also includes the families Maldanidae and Arenicolidae, but is now believed to only contain Echiura and family Capitellidae. Maldanidae and Arenicolidae have been moved to the clade Maldanomorpha
2. This family is traditionally placed in the order Sabellida, but is now considered to be closest to Cirratuliformia and as such is now unplaced
3. May be a suborder of Cryptostomata
4. Sometimes treated as a class