Phyllodesmium magnum
Rudman, 1991

Order: NUDIBRANCHIA
Suborder: AEOLIDINA
Family: Glaucidae

DISTRIBUTION

Known from tropical Western Pacific, and Western Australia. Records on the Forum show a widespread Indo-West Pacific distribution.

PHOTO

UPPER RIGHT: Kushimoto, Japan. PHOTO 36: 130mm long, July 1999. PHOTO 81: 100mm long, November 1999. PHOTOS: Yasuhiro Shirai.
LOWER PHOTOS: Noumea, New Caledonia, October 1988, 110mm long alive, Holotype. LEFT: Dorsal surface (left) of ceras and ventral surface (right), showing how the patches of zooxanthellae are concentrated on the upper (sunlit) side of each ceras. LOWER RIGHT: Showing disturbed animal which has cast off (autotomised) most of its cerata, showing the ridges on which the cerata are normally attached, and the position of the anal papilla (arrow). PHOTOS: Bill Rudman.

This is one of the larger species of Phyllodesmium, and from the branched arrangement of the digestive gland, flattened cerata, and position of zooxanthellae in the sunlit parts of the skin, it is most probably one of the species which retains zooxanthellae alive in its tissue so that it can benefit from their photosynthetic activity. See page on Solar-powered Sea Slugs for further detail.

All species of Phyllodesmium, feed on octocorals, and the defensive cnidosac found in other aeolids is absent. However, they have evolved an alternative defensive strategy. When attacked or disturbed their cerata can be cast off voluntarily, much like a lizard drops its tail. The autotomised cerata produce a sticky epithelial secretion and wriggle around vigorously for a considerable length of time after dropping off, apparently causing sufficient distraction to deter further interest in the now even more naked nudibranch.

This species probably feeds on, and obtains its zooxanthellae, from the soft coral Sinularia.

References:
• 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.

LOWER PHOTOS: Noumea, New Caledonia, October 1988, 110mm long alive, Holotype. LEFT: Dorsal surface (left) of ceras and ventral surface (right) showing how the patches of zooxanthellae are concentrated on the upper (sunlit) side of each ceras. LOWER RIGHT: Showing disturbed animal which has cast off (autotomised) most of its cerata, showing the ridges on which the cerata are normally attached, and the position of the anal papilla (arrow). PHOTOS: Bill Rudman.

Authorship details
Rudman, W.B., 1999 (November 22) Phyllodesmium magnum Rudman, 1991. [In] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/factsheet/phylmagn

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