Urochordata

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Urochordata (Tunicata) A subphylum of marine nonvertebrate chordates in which the body is typically enclosed in a protective tunic of a cellulose-like material and the notochord and dorsal hollow nerve cord are evident only in the free-swimming tadpole-like larval stage. The pharynx is specialized for filter feeding (see endostyle). There are three classes: the sessile Ascidiacea (sea squirts), the pelagic Thaliacea (salps), and the pelagic Larvacea (in which the larval form is retained into adulthood).

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