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.
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.
Class Sipuncula
Clade Pleistoannelida
Unplaced groups
Class Craniata
Subphylum Linguliformea
Subphylum Rhynchonelliformea
Class Gymnolaemata
Class Phylactolaemata
Class Stenolaemata
Unplaced groups
Class Eucycliophora
Dicyemida does not contain any established orders but does contain three families: Conocyemidae, Dicyemidae and Kantharellidae
Entoprocta has no orders but is split into four families; Barentsiidae, Pedicellinidae, Loxokalypodidae, and Loxosomatidae
The classes Planctosphaeroidea and Enteropneusta do not contain any orders
Class Pterobranchia
Class Cyclorhagida
Class Allomalorhagida
Unplaced groups
Loricifera has no classes and all species are contained within one order
Micrognathozoa has no classes and its single species is placed in one order
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
Class Dorylaimea
Class Chromadorea
Class Hoplonemertea
Class Palaeonemertea
Class Pilidiophora
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.
Orthonectida contains no classes or orders, but is split into two families; Pelmatosphaeridae and Rhopaluridae
Phoronida contains no classes, orders, or families, but is split into two genera; Phoronis and Phoronopsis
The class Catenulida contains no orders.
Subphylum Rhabditophora
Unplaced groups
Several stem group priapulid genera are not classified within any established orders. The orders listed below are solely crown priapulids.
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.
Superclass Eurotatoria
Clade Acanthocephala
The class Mesotardigrada contains one species, Thermozodium esakii, which has not been found since its reported discovery in 1937 and its existance is dubious. It is contained within the order Thermozodia.
The subphylum Xenoturbellida contains does not contain any classes or orders. It's only family is Xenoturbellidae which contains one genus, Xenoturbella.
The class Nemertodermatida does not contain any orders, but does contain two families; Ascopariidae and Nemertodermatidae.