Phyllodesmium opalescens
Rudman, 1991

Family: Glaucidae


Known only from Hong Kong - probably more widespread.


Hong Kong. LOWER LEFT: 12 Apr 1983 - S. Flat Reef, Tolo Channel. UPPER RIGHT: 12 Apr 1983 - S. Flat Reef, Tolo Channel. LOWER RIGHT: 14 Apr 1983 - E Pak Sha Chau, Mirs Bay. PHOTOS: Bernard Picton.

Characterised by a series of white marks down the midline and a bluish region near the end of the cerata, rhinophores and oral tentacles which are all capped with white or cream yellow. The radular morphology is also unique and the unbranched digestive gland duct in the cerata indicates that this species does not have a zooxanthellae symbiosis. I have no records of the length of living animals, but preserved specimens reach about 20mm.

• 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., 2001 (March 7) Phyllodesmium opalescens Rudman, 1991. [In] Sea Slug Forum. Australian Museum, Sydney. Available from

Related messages

Phyllodesmium opalescens from the Philippines

September 21, 2005
From: Jeff Rosenfeld

Hi Bill,
Here's a shot of Phyllodesmium opalescens taken in Anilao, Luzon Island, Philippines in April, 2004. As you suspected, its range is more widespread.

Locality: Anilao, Luzon Island, Philippines.Depth: 40 feet. Length: 12 mm. April, 2004. Photographer: Jeff Rosenfeld


Rosenfeld, Jeff, 2005 (Sep 21) Phyllodesmium opalescens from the Philippines. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Jeff,
This is a nice find. It certainly looks like P. opalescens, down to the broken white line down the dorsal midline. It certainly moves its potential geographic distribution down into the Indo-west Pacific proper.
Best wishes,
Bill Rudman

Rudman, W.B., 2005 (Sep 21). Comment on Phyllodesmium opalescens from the Philippines by Jeff Rosenfeld. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Phyllodesmium opalescens from South Korea

January 25, 2003
From: Dong Bum, Koh

Dear Dr.Bill,
I found this tiny nudibranch on gray sponges in Moon islet, on 14th Dec. 2002. Depth 15m. Water/Temp: 18 degrees. Photo: Dong Bum, Koh

I think it as Phyllodesmium serratum, as illustrated in Opisthobranchs of Izu Peninsula [:p159]
or a juvenile form of Sakuraeolis sp.

Can you please verify the ID.

Best regards,
From Dong Bum,Koh

Koh, D.B., 2003 (Jan 25) Phyllodesmium opalescens from South Korea. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from