plan·u·la /ˈplænjələ/
  浮浪幼體
  Plan·u·la n.; pl. Planulæ
  1. Biol. In embryonic development, a vesicle filled with fluid, formed from the morula by the divergence of its cells in such a manner as to give rise to a central space, around which the cells arrange themselves as an envelope; an embryonic form intermediate between the morula and gastrula. Sometimes used as synonymous with gastrula.
  2. Zool. The very young, free-swimming larva of the cœlenterates. It usually has a flattened oval or oblong form, and is entirely covered with cilia.
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  planula
       n : the flat ciliated free-swimming larva of hydrozoan
           coelenterates
       [also: planulae (pl)]