The sea urchin Heliocidaris tuberculata undergoes typical development, forming an echinoid pluteus larva, whereas H. erythrogramma undergoes direct development via a highly modified, nonfeeding larva. Using a polyclonal antibody prepared against yolk glycoproteins from the typical developer Stronglyocentrotus purpuratus, we found that H. tuberculata contains cross-reactive proteins in abundance, but H. erythrogramma does not. In addition, we used immunoelectron microscopy to demonstrate that unfertilized eggs of H. tuberculata contain yolk platelets, but those of H. erythrogramma do not.