Solar Panel Sea Slug

Phyllodesmium longicirrum is probably the most spectacular of the aeolids which have evolved a symbiotic relationship with single-celled plants (zooxanthellae). It is exceptionally large, often more than 12cm long, and the cerata have evolved into large flattened "solar paddles" to maximise the animal's ability to "farm' the plants in its body.

It is known to feed on the soft-coral Sarcophyton, but we don't know if it eats other soft corals. It obviously has a symbiotic relationship with zooxanthellae but we can only guess that it gets the zooxanthellae from Sarcophyton. Like all species of Phyllodesmium, this species lacks the defensive cnidosacs usually found in aeolids. Coll et al (1985) have shown that it stores the diterpene trocheliophorol in its cerata. This distasteful, if not toxic, chemical is obtained from it food, the soft coral Sarcophyton trocheliophorium and is possibly an alternative way to protect it from predators.