This is by far one of my favorite animals collected on the expedition, I did not even knew these existed!
This slug's sequesters/hosts single celled, algae as symbionts in its cerata (the fuzzy bits on its back). The symbiosis is a mutualism: dinoflagellates from the genus Symbiodinium get raw materials required for photosynthesis and a safe place to live with full access to sunlight inside the slug's body. In return the dinos donate some portion of the sugars they generate from photosynthesis to the slug, meaning that most of the slug's food is generated inside its body!
(Explanation courtesy of Dr. Michele Weber)
Diving Safety Officer
California Academy of Sciences