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Urochordata Lankester, 1877 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 ).
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 lancelets were traditionally seen as the sister lineage to the vertebrates; in turn, these two groups together (sometimes called Notochordata) were considered the sister group to the Tunicata (also called Urochordata and including sea squirts).
Olfactores is a clade within the Chordata that comprises the Tunicata (Urochordata) and the Vertebrata [citation needed] (sometimes referred to as Craniata).Olfactores represent the overwhelming majority of the phylum Chordata, as the Cephalochordata are the only chordates not included in the clade.
Agnatha (/ ˈ æ ɡ n ə θ ə, æ ɡ ˈ n eɪ θ ə /; [3] from Ancient Greek ἀ-(a-) 'without' and γνάθος (gnáthos) 'jaws') is a paraphyletic infraphylum [4] of non-gnathostome vertebrates, or jawless fish, in the phylum Chordata, subphylum Vertebrata, consisting of both living (cyclostomes) and extinct (conodonts, anaspids, and ostracoderms, among others).
The Doliolida are an order of small marine chordates of the subphylum Tunicata.They are in the class Thaliacea, which also includes the salps and pyrosomes. [1] [2] The doliolid body is small, typically 1–2 mm long, and barrel-shaped; it features two wide siphons, one at the front and the other at the back end, and eight or nine circular muscle strands reminiscent of barrel bands.
Ascidiacea, commonly known as the ascidians or sea squirts, is a paraphyletic class in the subphylum Tunicata of sac-like marine invertebrate filter feeders. [2] Ascidians are characterized by a tough outer test or "tunic" made of the polysaccharide cellulose.
Although many planktonic organisms are bioluminescent, pyrosome bioluminescence is unusual in its brilliance and sustained light emission, [10] and evoked the following comment when seen by the eminent scientist Thomas Huxley at sea: