Tunicates (subphylum Tunicata) are a group of filter-feeding marine invertebrates. As chordates, they have been proposed to be the closest relatives of vertebrates. Tunicates are divided into three classes: the sessile Ascidiacea, and the free-swimming Thaliacea and Appendicularia. Some anatomical features are shared between classes, while others are specific to a lineage or to a life stage.
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