• (a.) Having the spines of the dorsal fin unsymmetrical, or thickened alternately on the right and left sides.
Het'er·a·canth adjective [ Hetero- + Greek ... a spine.] (Zoology) Having the spines of the dorsal fin unsymmetrical, or thickened alternately on the right and left sides. 
heteracanth Having the spines of the dorsal and anal fins alternately broader on one side than the other.