Which characteristic is or characteristics, are shared, by both cnidarians and flatworms? 14. a. dorsoventrally flattened bodies b. true muscle c. radial symmetry d. a digestive system with a single opening e· two ofthese 15. All of the following are characteristics of arthropods EXCEPT a. an exoskeleton b. numerous species c. jointed appendages d. a diversity of gas exchange structures e. a dorsal nerve cord Which molluscan class includes the most “intelligent” invertebrates? a. Polyplacophora b. Bivilvia c. Cephalopoda d. Gastropoda 16. e. Both ‘b’ and ‘e’ are equally intelligent Which of the following in the phylum Annelida is medically importan a. Oligochaeta b. Polychaeta c. Hirudinea d. Two of the above 17. e. All of the above Which of the molluscan class includes members that undergo embryonic torsion? a. Polyplacophora b. Bivilvia c. Cephalopoda d. Gastropoda e. All molluscan classes have this characteristic 18. Which of the following in the phylum Annelida have parapodia? a. Oligochaeta b. Polychaeta c. Hirudinea d. Two of the above e. All of the above 19.