On 17 March 2010, I collected 4 adult red urchins, Strongylocentrotus franciscanus, from the Lighthouse Island channel, near Charleston, OR, during low tide. They were found in burrows, holes in the rocky outcroppings created by repetitive scraping by their spines and teeth, alongside some purple urchins, S. purpuratus. This is a relatively rare find, because S. franciscanus is mostly subtidal. Red urchins have longer spines and tube feet, as well as a larger test diameter compared to purple urchins, and often they are more reddish than purple. In my Comparative Embryology Class, we were looking at the development of S. purpuratus and I was interested to follow the development of a closely related species. I induced spawning in the adult urchins in the lab by injecting them with 5 ml of 0.5 M potassium chloride. I then collected eggs and sperm, and started a culture that afternoon. According to Strathmann (1987), S. purpuratus eggs range from 78 to 80 µm, while eggs of S. franciscanus are between 130 and 140 µm. The eggs I fertilized averaged 125 µm in diameter (n=10) and the fertilization envelope expanded in about a minute after addition of sperm to eggs. It raised about 18 µm (n=10) from the surface of the eggs. After 16 hours at 13°C, the embryos reached the blastula stage shown here. The fertilization envelope is still seen around the blastula, which rotates within the envelope. Eggs of S. purpuratus would take over 20 hours to reach the blastula stage at the same temperature.
Strathmann, M. 1987. Phylum Echinodermata, Class Echinoidea. In Reproduction and Development of Marine Invertebrates of the Northern Pacific Coast. P. 512. University of Washington Press, Seattle.