http://en.wikipedia.org/wiki/Ascidiacea
The larva possesses a long tail, containing a hollow dorsal nerve tube and a notochord, both features clearly indicative of the animal's chordate affinities. The nerve tube enlarges in the main body, and will eventually become the cerebral ganglion of the adult. The tunic develops early in embryonic life, and extends to form a fin along the tail in the larva. The larva also has a statocyst and a pigmented cup above the mouth, which opens into a pharynx lined with small clefts opening into a surrounding atrium. The mouth and anus are originally at opposite ends of the animal, with the mouth only moving to its final (posterior) position during metamorphosis.
The larva possesses a long tail, containing a hollow dorsal nerve tube and a notochord, both features clearly indicative of the animal's chordate affinities. The nerve tube enlarges in the main body, and will eventually become the cerebral ganglion of the adult. The tunic develops early in embryonic life, and extends to form a fin along the tail in the larva. The larva also has a statocyst and a pigmented cup above the mouth, which opens into a pharynx lined with small clefts opening into a surrounding atrium. The mouth and anus are originally at opposite ends of the animal, with the mouth only moving to its final (posterior) position during metamorphosis.
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