The Sea Urchin is also known as Echinoidea. Sea Urchins reproduce sexually. The male releases sperm into the water and the female releases million of eggs into the water. The sperm and the eggs fuse to fertilize the egg. The sperm and the eggs usually fuse outside of the female's body, but in some rare cases they can fuse inside the female's body. Once the egg is fertilized, a larvae is formed. The larvae is known as a pluteus. The larvae goes through stages of development until it eventually develops into an adult sea urchin.
This picture shows a sea urchin releasing gametes into the ocean water. The gametes are the white dots on top of the sea urchin.