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Bilateria (/ ˌ b aɪ l ə ˈ t ɪər i ə /) [5] is a large clade of animals characterised by bilateral symmetry during embryonic development. This means their body plans are laid around a longitudinal axis with a front (or "head") and a rear (or "tail") end, as well as a left–right–symmetrical belly ( ventral ) and back ( dorsal ) surface.
The relative number of species contributed to the total by each phylum of animals. Arthropoda is the phylum with the most individual organisms. 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 ...
The remaining animals, the great majority—comprising some 29 phyla and over a million species—form the Bilateria clade, which have a bilaterally symmetric body plan. The Bilateria are triploblastic , with three well-developed germ layers, and their tissues form distinct organs .
' second mouth ') are bilaterian animals of the superphylum Deuterostomia (/ ˌ dj uː t ər ə ˈ s t oʊ m i. ə /), [3] [4] typically characterized by their anus forming before the mouth during embryonic development. Deuterostomia comprises three phyla: Chordata, Echinodermata, Hemichordata, and the extinct clade Cambroernida.
In the past, some zoologists grouped bilaterian animal phyla based on characteristics related to the coelom for practical purposes, knowing, and explicitly stating, that these groups were not phylogenetically related. Animals were classified in three informal groups according to the type of body cavity they possess, in a non-taxonomic ...
Animals with bilateral symmetry are classified into a large group called the bilateria, which contains 99% of all animals (comprising over 32 phyla and 1 million described species). All bilaterians have some asymmetrical features; for example, the human heart and liver are positioned asymmetrically despite the body having external bilateral ...
Nephrozoa is a major clade of bilaterian animals. It includes all bilaterians other than Xenacoelomorpha . It contrasts with the Xenambulacraria hypothesis, which instead posits that Xenacoelomorpha is most closely related to Ambulacraria .
The following is a list of the classes in each phylum of the kingdom Animalia. There are 107 classes of animals in 33 phyla in this list. However, different sources give different numbers of classes and phyla. For example, Protura, Diplura, and Collembola are often considered to be the three orders in the class Entognatha. This list should by ...