Flatworms See the Light
Symsagittifera roscoffensis is a small marine flatworm. During its early development, a certain green alga – Tetraselmis convolutae – invades the worm’s tissues, stimulating a dramatic physiological conversion: losing the ability to feed independently.
The algae embed themselves near the surface of the worm’s transparent body, finding optimal spots to catch sunlight. Via photosynthesis, alga feed the worm oxygen and sugar while the worm provides nitrogen and a comfortable home. The worm’s behavior is altered by such intimate integration, as it prefers sunny locations on the beach to optimize photosynthetic opportunities for its cohort.