One of the common arguments why the process of transplanting non-human organs which came from animals may be considered as an ethical act is that antigens on the surface of the non-human organs are not significantly rejected in the process. Although its research is still substantial, it is still considered as a matter of ethical issue.
Sharp teeth that are constantly replaced would be the answer! In order for it to be a specific adaptation you would need the detail of why the animal has that adaption for example fins for stability:)
External skeleton is the correct answer. Hope this helps out !