Terry Catches a Ray-Finned Fish from the Ocean and Notices

Multiple Choice

Terry catches a ray-finned fish from the ocean and notices that attached to its flank is an equally long, snakelike organism. The attached organism has no external segmentation, no scales, a round mouth surrounded by a sucker, and two small eyes. Terry concludes it is a hagfish.
Terry saved some of the tooth-like objects within the hagfish's round mouth to analyse their composition in his mentor's biochemistry research lab. Terry will find that they are composed of the same protein found in tetrapod ________.

A) scales
B) teeth
C) bones
D) cartilage