Onvoluta worms hatch in early spring. They crawl about in the mud feeding on algae, which find their way into the skin of the worms. There they prosper as they worms feed on the sun-warmed surface mud.

The worms become greener and greener as they mature. Gradually their mouths seal shut, leaving only an internal garden of algae to provide them with food. As winter approaches, their food supply is exhausted, and the worms grow pale again. They lay their eggs in the mud just before they starve to death.

How do you think both worms and algae benefit from this relationship? WHY??