Source : Webster's Revised Unabridged Dictionary (1913)

Urochord \U"ro*chord\, n. [2d uro- + chord.] (Zo["o]l.)
   The central axis or cord in the tail of larval ascidians and
   of certain adult tunicates. [Written also {urocord}.]

Source : WordNet®

urochord
     n 1: primitive marine animal having a saclike unsegmented body
          and a urochord (a notochord) conspicuous in the larva
          [syn: {tunicate}, {urochordate}]
     2: a notochord of a larval tunicate typically confined to the
        caudal region