How does multicellularity evolve? Scientists who study a family of green algae that includes unicellular Chlamydomonas and multicellular Volvox are beginning to find answers to this question.

“Our findings show that the genetic underpinnings of cell-to-cell cohesion and segregation—the ability for different cells to sort themselves into separate regions within a multicellular mass—existed ...

zooxanthellæ are abundantly present within the cells of the digestive glands. Here then is another animal digesting intracellularly and harbouring a unicellular green alga within its tissues.