Planula

2 definitions found

From The Collaborative International Dictionary of English v.0.48 [gcide]:

  Planula \Plan"u*la\, n.; pl. {Planul[ae]}. [L., a little plane.]
     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}.
        [1913 Webster]
  
     2. (Zool.) The very young, free-swimming larva of the
        c[oe]lenterates. It usually has a flattened oval or oblong
        form, and is entirely covered with cilia.
        [1913 Webster]

From WordNet (r) 2.0 [wn]:

  planula
       n : the flat ciliated free-swimming larva of hydrozoan
           coelenterates
       [also: {planulae} (pl)]