Thaliacea

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Thaliacea (salps; phylum Chordata, subphylum Urochordata) A class of tunicates in which two siphons occur at opposite ends of the body, so the current of water passing through the animal is used for gas exchange, feeding, and also for locomotion. Salps are adapted for a free-swimming, planktonic existence. There are six genera, most occurring in tropical or subtropical seas.