Model Organism: Sea Urchins
Sea urchins (Strongylocentrotus purpuratus and Lytechinus pictus) are found in coastal ocean waters. They produce prodigious numbers of eggs and sperm that undergo fertilization in the ocean. The eggs and sperm of sea urchins closely match those of human eggs and sperm in size, and urchin eggs have clear membranes. Because urchin and human embryos are very similar in their early developmental stages, scientists have used urchins as a model to study fertilization.