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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.
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.
Tunicates (subphylum Tunicata) are a group of filter-feeding marine invertebrates. [1] As chordates , they have been proposed to be the closest relatives of vertebrates . [ 2 ] Tunicates are divided into three classes: the sessile Ascidiacea , and the free-swimming Thaliacea and Appendicularia . [ 1 ]
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).
Invertebrates cells fire in response to similar stimuli as mammals, such as tissue trauma, high temperature, or changes in pH. The first invertebrate in which a neuron cell was identified was the medicinal leech, Hirudo medicinalis. [14] [15] Learning and memory using nociceptors have been described in the sea hare, Aplysia.
Vertebrates (phylum Chordata), particularly pelagic fish, cetaceans and sea turtles, form the largest contribution; these animals have endoskeletons made of bones and cartilages and propel themselves via a powerful tail and fan/paddle-shaped appendages such as fins, flippers or webbed feet.
[73] [74] More recently, the fundamental symmetric and twisted development of vertebrates is the topic of the axial twist theory. According to this theory, there is a deep agreement between the vertebrates and cephalochordates, and even all chordates. [75] [76]
It is traditionally considered as transitional fossil between invertebrates and vertebrates, [3] and considered as stem-group chordate in 2012. [ 4 ] [ 5 ] It was a primitive creature with no evidence of eyes, without a well defined head, and less than 2 inches (5 centimetres) long.