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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).
The calcichordate hypothesis, formulated by British Museum paleontologist Richard Jefferies, holds that each separate lineage of chordate (Cephalochordates, Urochordates, Craniates) evolved from its own lineage of mitrate, and thus the echinoderms and the chordates are sister groups, with the hemichordates as an out-group. [1]
Pegea confederata on a 1995 stamp from Azerbaijan. A salp (pl.: salps, also known colloquially as “sea grape”) or salpa (pl.: salpae or salpas [2]) is a barrel-shaped, planktonic tunicate in the family Salpidae.
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.
The endostyle is an organ found in invertebrate chordate species of tunicates, lancelets, and in the larval stage of vertebrate lampreys.It assists in filter-feeding. [1] It has evolved into the thyroid in vertebrate chordates.