RNA sequencing of spines from four diverse sea urchin species (H.</p><p>pulcherrimus, E.tribuloides, Lytechinus variegatus, Strongylocentrotus purpuratus) to examine shared core gene families. share core gene families. Significant orthologs include the spicule matrix genes originally identified in larval skeletons. Spines from these four species also show divergence in a variety of orthogroups.