Phyllodesmium longicirrum
(Bergh, 1905)

Family: Glaucidae


Known from the Indonesian Archipelago to the Great Barrier Reef, Australia.


RIGHT: Animal (10cm long) crawling over Porites colony. Indonesia.
LOWER LEFT: Ceras showing the white ducts of the digestive gland radiating out to the brown "gardens" of symbiotic zooxanthellae. PHOTO: Bill Rudman.
LOWER RIGHT: Section through the a ceras showing the ducts leading to the zooxanthellae "gardens" at the surface of the ceras. (zooxanthellae stained red.) PHOTO: Bill Rudman.


Solar-powered Sea Slugs

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 [see Solar-powered Sea Slug Page] 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 ptotect it from predators.

• Coll, J.C., Bowden, B.F., Tapiolas, D.M., Willis, R.H., Djura, P.. Streamer, M. & Trott, L. (1985) Studies of Australian soft corals - XXXV. The terpenoid chemistry of soft corals and its implications. Tetrahedron, 41(6): 1085-1092.
• Rudman, W.B. (1981) The anatomy and biology of alcyonarian feeding aeolid opisthobranch molluscs and their development of symbiosis with zooxanthellae. Zoological Journal of the Linnean Society, 72: 219-262.
• Rudman, W.B. (1991) Further studies on the taxonomy and biology of the octocoral-feeding genus Phyllodesmium Ehrenberg, 1831 (Nudibranchia: Aeolidoidea). Journal of Molluscan Studies, 57(2): 167-203.

Authorship details
Rudman, W.B., 1998 (October 11) Phyllodesmium longicirrum (Bergh, 1905). [In] Sea Slug Forum. Australian Museum, Sydney. Available from

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