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A chordate (/ ˈ k ɔːr d eɪ t / KOR-dayt) is a deuterostomal bilaterian animal belonging to the phylum Chordata (/ k ɔːr ˈ d eɪ t ə / kor-DAY-tə).All chordates possess, at some point during their larval or adult stages, five distinctive physical characteristics (synapomorphies) that distinguish them from other taxa.
The body plan of hemichordates is characterized by a muscular organization. The anteroposterior axis is divided into three parts: the anterior prosome, the intermediate mesosome, and the posterior metasome. The body of acorn worms is worm-shaped and divided into an anterior proboscis, an intermediate collar, and a posterior trunk.
The evolution of the notochord within the phylum Chordata is considered in detail by Holland and Somorjai (2020). Vertebrates now have spines so they do not need a notochord. [26] The following organisms retain a post-embryonic notochord: Acipenseriformes (paddlefish and sturgeon) [27] Lancelet (Amphioxus) Tunicate (larval stage only) Hagfish ...
A tunicate is an exclusively marine invertebrate animal, a member of the subphylum Tunicata (/ ˌ tj uː n ɪ ˈ k eɪ t ə / TEW-nih-KAY-tə).This grouping is part of the Chordata, a phylum which includes all animals with dorsal nerve cords and notochords (including vertebrates).
Branchiostoma belcheri exhibit all basic characteristics of the Chordata phylum including the notochord, dorsal nerve cord, pharynx, buccal cavity, cirri, tail, dorsal fin, nerve cord, segmented muscle, and ocelli. Starting with the internal structure, said organisms have true coeloms where the critical organs develop.
Many taxa (for example the molluscs) have some form of serial repetition in their units but are not conventionally thought of as segmented. Segmented animals are those considered to have organs that were repeated, or to have a body composed of self-similar units, but usually it is the parts of an organism that are referred to as being segmented ...
In 1811, Jean-Baptiste Lamarck defined the vertebrates as a taxonomic group, [2] a phylum distinct from the invertebrates he was studying. [42] He described them as consisting of four classes, namely fish, reptiles, birds, and mammals, [ 43 ] but treated the cephalochordates and tunicates as molluscs . [ 42 ]
In addition, segmented muscle blocks and parts of the nervous system are asymmetrical. [44] After metamorphosis the anatomy becomes more symmetrical, but some asymmetrical traits are still present also as adults, such as the nervous system and the location of the gonads which are found on the right side in Asymmetron and Epigonichthys (in ...