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A 'planula' is the free-swimming, flattened, ciliated, bilaterally symmetric larva of a jellyfish, a hydrozoan cnidarian, or a ctenophore. Depending on the species, the planula either metamorphosises into a miniature version of the adult form (such as some jellyfish and all ctenophores), or navigates through the water until it reaches a hard substrate (some may prefer specific substrates) where it anchors and grows into a polyp. Planulae of Medusozoa have no mouth or digestive tract and are unable to feed themselves, while those of Anthozoa can feed.