polymorphosis

from The Collaborative International Dictionary of English v.0.48

Polymorphosis \Pol`y*mor*pho"sis\, n. [NL. See {Poly-}, and
   {Morphosis}.] (Zool.)
   The assumption of several structural forms without a
   corresponding difference in function; -- said of sponges,
   etc.
   [1913 Webster]