Codium bursa

If you have ever been in the Mediterranean it is possible that you have found some "hairy green balls" in the shoreline. They just happen to be this strange Mediterranean macroalga. They apparently fill in with water and they perform photosynthesis but this ability declines with increasing size.
Some interesting facts here:
https://www.veterinariadigital.com/en/post_blog/codium-bursa-example-of-nutritional-transfer-between-minerals-and-animals-dissemination-105th/