Consider the cladogram. A cladogram is shown. Mollusks, echinoderms, chordates, and annelids have roundworms as a common ancestor. According to the cladogram, which organisms have roundworms as a common ancestor? mollusks and flatworms sponges and chordates flatworms, sponges, and cnidarians mollusks, echinoderms, chordates, and annelids