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| name=Tunicate | image=Tunicate komodo.jpg | image_caption= Gold-mouth sea squirt (''Polycarpa aurata'') | image_width=250px | regnum=Animalia | phylum=Chordata | subphylum=Tunicata | subphylum_authority=Lamarck 1816 | subdivision_ranks=Classes〔〔 | subdivision= *Ascidiacea *Thaliacea *Larvacea | synonyms=Urochordata Lankester 1877 }} A tunicate is a marine invertebrate animal, a member of the subphylum Tunicata, which is part of the Chordata, a phylum which includes all animals with dorsal nerve cords and notochords. The subphylum was at one time called Urochordata, and the term urochordates is still sometimes used for these animals. Some tunicates live as solitary individuals, but others replicate by budding and become colonies, each unit being known as a zooid. They are marine filter feeders with a water-filled, sac-like body structure and two tubular openings, known as siphons, through which they draw in and expel water. During their respiration and feeding, they take in water through the incurrent (or inhalant) siphon and expel the filtered water through the excurrent (or exhalant) siphon. Most adult tunicates are sessile and are permanently attached to rocks or other hard surfaces on the ocean floor; others, such as salps, doliolids and pyrosomes, swim in the pelagic zone of the sea as adults. Various species are commonly known as sea squirts, sea pork, sea livers, or sea tulips. The earliest unequivocal species of tunicate appeared in the fossil record in the early Cambrian period. Despite their simple appearance and very different adult form, their close relationship to the vertebrates is shown by the fact that during their mobile larval stage, they possess a notochord or stiffening rod and resemble a tadpole. Their name derives from their unique outer covering or "tunic" which is formed from proteins and carbohydrates and acts as an exoskeleton. In some species, it is thin, translucent, and gelatinous, while in others it is thick, tough, and stiff. ==Taxonomy== About 2,150 species of tunicates occur in the world's oceans, mostly living in shallow water. The most numerous group is the ascidians, and fewer than 100 species of these are found at depths greater than .〔 Some are solitary animals leading a sessile existence attached to the seabed, but others are colonial and a few are pelagic. Some are supported by a stalk, but most are attached directly to the substrate, which may be a rock, shell, coral, seaweed, mangrove root, dock, piling, or ship's hull. They are found in a range of solid or translucent colours and may resemble seeds, grapes, peaches, barrels, or bottles. One of the largest is a stalked sea tulip, ''Pyura pachydermatina'', which can grow to be over a metre (yard) tall.〔 The Tunicata were established by Jean-Baptiste Lamarck in 1816. In 1881, Francis Maitland Balfour introduced a second name for the same group, "Urochorda", to emphasize the affinity of the group to other chordates.〔Foster, M. (ed.); Sedgwick, Adam (ed.); The Works of Francis Maitland Balfour. Vol. III. Memorial edition. Pub: Macmillan and co. 1885. May be downloaded from ()〕 No doubt largely because of his influence, various authors supported the term, either as such, or as "Urochordata", but the usage is invalid because "Tunicata" has precedence and grounds for superseding the name never existed. Accordingly, the current (formally correct) trend is to abandon the name Urochorda or Urochordata in favour of the original Tunicata, and the name Tunicata is almost invariably used in modern scientific works. It is accepted as valid by the World Register of Marine Species〔(Tunicata ) World Register of Marine Species. Retrieved 2011-11-12.〕 and by the Integrated Taxonomic Information System.〔(Tunicata Lamarck, 1816 ) Integrated Taxonomic Information System. Retrieved 2011-11-12.〕 Various common names are used for different species. Sea tulips are tunicates with colourful bodies supported on slender stalks.〔(【引用サイトリンク】title=Sea squirts and sea tulips )〕 Sea squirts are so named because of their habit of contracting their bodies sharply and squirting out water when disturbed.〔(【引用サイトリンク】title=Sea squirt )〕 Sea liver and sea pork get their names from the resemblance of their dead colonies to pieces of meat.〔(【引用サイトリンク】title=Sea pork, ''Aplidium stellatum'' )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Tunicate」の詳細全文を読む スポンサード リンク
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