Polygordius \Pol`y*gor"di*us\, n. [NL. See {Poly-}, and {Gordius}.] (Zo["o]l.) A genus of marine annelids, believed to be an ancient or ancestral type. It is remarkable for its simplicity of structure and want of parapodia. It is the type of the order Archiannelida, or Gymnotoma. See {Loeven's larva}.