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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.
Another feature present in both the Hemichordata and Chordata is pharyngotremy — the presence of spiracles or gill slits into the pharynx, which is also found in some primitive fossil echinoderms . [17] [18] A hollow nerve cord is found in all chordates, including tunicates (in the larval stage). Some hemichordates also have a tubular nerve cord.
This article contains a list of all of the classes and orders that are located in the Phylum Chordata. The subphyla Tunicata and Vertebrata are in the unranked Olfactores clade, while the subphylum Cephalochordata is not. Animals in Olfactores are characterized as having a more advanced olfactory system than animals not in it.
All chordates share a common ancestor which lost its echinoderm stereom calcite skeleton. However, later revisions of the theory had each separate lineage losing its calcitic skeleton independently, [ 6 ] as it evolved from its own mitrate ancestor, making the chordates a paraphyletic group [ citation needed ] .
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).
Segmentation in chordates is characterized as the formation of a pair of somites on either side of the midline. This is often referred to as somitogenesis. In vertebrates, segmentation is most often explained in terms of the clock and wavefront model.
Lampreys contain these characteristics that define them as chordates. Lamprey anatomy is very different based on what stage of development they are in. [ 80 ] The notochord is derived from the mesoderm and is one of the defining characteristics of a chordate.
The main deuterostome phyla are the Ambulacraria and the Chordata. [143] Ambulacraria are exclusively marine and include acorn worms , starfish , sea urchins , and sea cucumbers . [ 144 ] The chordates are dominated by the vertebrates (animals with backbones ), [ 145 ] which consist of fishes , amphibians , reptiles , birds , and mammals .