Aeolidiella stephanieae - zooxanthella for orientation?

December 11, 2007
From: Dene Banger

We are a Canadian commercial aquaculture company breeding the nudibranch Aeolidella stephanieae for the aquarium trade (well known as  Berghia verrucicornis in the industry). Upon careful observation of their behaviour, feeding patterns, mating patterns etc., we are beginning to think that the retention of zooxanthella in the central digestive glands or cerata may be used for orientation. For example, increased or high stimulation of the zooxanthella in the cerata by light would indicate to the nudibranch that it is a) "right-side" up
b) that it is traveling along the top side of a physical object.

Likewise, less stimulation would indicate that the nudibranch was either inverted or travelling on the underside of an object.

I have read Steve Kempf's suggestion concerning solar-powered sea slugs and believe that there is some merit to a theory of, zooxanthella for orientation.

Incidently, we designed our breeding/hatching tanks along this idea and have documented six pairs of adults consistently laying 70 eggs strings in a 10 day period (approx. 6.8-7.2 strings per day). Certainly, well above most reports of an eggstring every 4-7 days. Upon hatching we are witnessing several thousand larvae in our specialized hatchers.

We are wondering if there has been more work done on the function of zooxanthella in this organism, and would invite some thoughts around such.

Dene Banger President
Sea Life Aquaculture Inc., Canada

Banger, D.B., 2007 (Dec 11) Aeolidiella stephanieae - zooxanthella for orientation?. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Dene,

It is certainly an interesting idea to suggest they have acquired zooxanthellae so they know which way is up, but one question you would need to ask is why every other mollusc without zooxanthellae finds their statocysts sufficient for the task. A number of other animal groups have developed similar symbioses with zooxanthellae, such as the reef-forming corals, and it seems those without zooxanthellae seem able to grow 'upwards' without the assistance of zooxanthellae.

I am not sure what you mean when you say you have designed your breeding/hatching tanks in accord with this idea. If you mean you have done everything to maximise photosynthesis for the zooxanthellae I assume that will keep the adult nudibranchs in good condition because a healthy stock of zooxanthellae in their tissues is just what the nudibranch needs, as it takes sugars and other nutrients from the zooxanthellae for its own needs.

Have a look at the zooxanthellae in nudibranchs page and the solar-powered nudibranch page. They will give you some background information and links to more.

Best wishes,
Bill Rudman

Rudman, W.B., 2007 (Dec 11). Comment on Aeolidiella stephanieae - zooxanthella for orientation? by Dene Banger. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

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