Um, coral has photosynthetic zooxanthellae, which it is dependent upon. (No zooxanthellae = “bleaching”)
Also, almost all clams have zooxanthellae in their mantles. So this is nothing really new, and the reporter’s claim of “Now researchers have found one animal that does just that,” as if it had never existed in any animal until now, is false. What IS new is that I believe this is the first nudibranch discovered that has this sort of symbiotic relationship with algae.
This is different. Zooxanthellae are a separate organism from the coral that lives symbiotically with them. This sea slug only takes the chloroplasts from the plant cells and uses them. The tricky bit is that the chloroplasts generally require the rest of the plant cell to be able to survive, but the sea slug has DNA which creates the needed proteins and it appears that it might have incorporated the plant's DNA into its own.