I found this on the web:


Starfish spawn which means they release eggs and sperm into the open ocean at the same time. Females can produce up to 65 million eggs per spawning season. During spawning season thousands of starfish gather and release sperm and eggs into the ocean. The egg and sperm join and produce many tiny sea stars which float in the water like little blobs that later form into a star shape.
They can also asexually reproduce. They also can regenerate their body. If another creature attacks the starfish and eats or tears off an arm they can regenerate arms. As long as the main body is not injured they can re-grow.