The sea urchin can be one of the smallest marine animals in the ocean. Along with the starfish they are both part of the Echinodermata phylum. Along with the sea star it is difficult to differentiate the sex of a sea urchin. The sea urchin is an external fertilizer meaning that the sperm and egg come together outside of the female’s body. The male sea urchin releases the sperm and the female urchin releases millions of eggs. The sperm first step in the reproductive system is to go through the jelly coat of the egg in order to reach the egg. Once it does the eggs start to divide and multiply rapidly. At this point the eggs reach a state of gaining a skeleton than later starts to begin maturing. After five years the urchin matures and then it begins the reproductive system over again. This is the reproductive system of this small animal.