The slow block to polyspermy in the sea urchin embryo consists of a physical barrier to further sperm penetration into the egg. The physical barrier is the fertilization envelope, which lifts off of the egg surface first at the site of sperm entry.



Fertilization envelope elevation in Lytechinus pictus. Images from a movie courtesy of the Exploratorium .

Click the thumbnails to see movies of fertilization envelope production in the Pacific urchin, Lytechinus pictus (left, center) and Paracentrotus lividus.
Fertilization in Lytechinus pictus (0.8 Mb). Courtesy of the Exporatorium.
Fertilization in Lytechinus pictus (0.8 Mb). Courtesy of the Exporatorium.
Fertilization in Lytechinus pictus (0.4 Mb). Produced by Ted Shinners and Jeff Hardin.
Fertilization in Lytechinus pictus (0.4 Mb). Produced by Ted Shinners and Jeff Hardin.
Fertilization in Paracentrotus lividus (0.4 Mb). Courtesy of Christian Gache and Thierry Lepage, Villefranche-sur-Mer.
Fertilization in Paracentrotus lividus (0.4 Mb). Courtesy of Christian Gache and Thierry Lepage, Villefranche-sur-Mer.