Source : Webster's Revised Unabridged Dictionary (1913)

Syllidian \Syl*lid"i*an\, n. [From NL. Syllis, the typical
   genus.] (Zo["o]l.)
   Any one of numerous species of marine annelids of the family
   {Syllid[ae]}.

   Note: Many of the species are phosphorescent; others are
         remarkable for undergoing strobilation or fission and
         for their polymorphism. The egg, in such species,
         develops into an asexual individual. When mature, a
         number of its posterior segments gradually develop into
         one or more sexual individuals which finally break away
         and swim free in the sea. The males, females, and
         neuters usually differ greatly in form and structure.