Zooxanthellae in nudibranchs
Pteraeolidia ianthina. Upper photo showing section of body. The brown lines across the body and down the cerata are ducts filled with brown zooxanthellae. Lower photo is a section through a ceras to show the numbers of zooxanthellae that can pack into the body of a nudibranch host animal. Scale = 40 microns. Photos: Bill Rudman.
Many nudibranchs have evolved symbiotic partnerships with zooxanthellae. Some nudibranch species get their zooxanthellae by eating cnidarians in which the zooxanthellae are already living, but how some obtain them is still a mystery. Many nudibranchs with symbiotic algae have greatly modified the shape of their body to provide as many sunlit regions as possible for their 'guest workers' to photosynthesise.
Rudman, W.B., 2000 (October 10) Zooxanthellae in nudibranchs. [In] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/factsheet/zoox3