Answer
Lampreys have soft, cartilaginous skeletons unlike conodonts with their mineralized dental tissues. It then makes sense that lampreys attach to hosts and act as parasites, sucking fluid from their hosts, while conodonts could use their mineralized tissues to crush and chop food.
Work Step by Step
Think about how you eat now (mineralized dental tissues) compared to how that would work/what you would have to eat if you jaw and teeth were turned in to cartilage (of the hardness of your nose or ears).
