Echinoid skeleton: absence of a collagenous matrix

Lack of hydroxyproline and proline in the calcified distal spines and Aristotle's lantern of the echinoderm Strongylocentrotus indicated the absence of a collagenous matrix. The fact that the small amount of collagen present in the base of the spines and in the test with sutures was removed by bacterial collagenase indicates that this collagen was not calcified.