A carbohydrate-based mechanism of species recognition in sea urchin fertilization. P.A.S. Mourão. Braz J Med Biol Res 2007; 40: 5-17.  

Figure 7. Phylogenetic relationship and divergence times of some sea urchin species and a summary of the structure of the polysaccharides from their egg jelly. Possibly, the carbohydrate-mediated mechanism of egg-sperm recognition played a direct role in the separation of S. droebachiensis from S. pallidus. The bindin mechanism may have functioned as an isolation mechanism on the earlier separation of the joint lineage from S. purpuratus. Myr = million years of evolutionary divergence. Data modified from Biermann et al. (50) (printed with permission from Blackwell Publishing).