Urochordata, also known as tunicates or sea squirts, are a subphylum of chordates that have a notochord only during their larval stage. They are filter feeders that live in aquatic or marine environments and have a u-shaped gut. Most urochordates are hermaphrodites and can reproduce both sexually and asexually through budding. They lack a brain and have a simple nervous system consisting of a nerve cord.