Phyllodesmium? from Sth Africa

December 6, 1999
From: Valda Fraser

Dear Bill,
Any help with this white aeolidacea?

Locality: South Coast of Kwa Zulu Natal South Africa near Port Shepstone
Low profile scattered rocky reef, Depth: 16 - 18m, April 1999. Size: 60mm

Valda Fraser.

Fraser, V., 1999 (Dec 6) Phyllodesmium? from Sth Africa. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Valda,
I think this is a species of Phyllodesmium. One possibility is Phyllodesmium horridum Macnae, 1954, which was described as translucent white with opaque white line down midline and pinkish body organs showing through. Cerata have iridescent blue and lilac tinge and brown duct of digestive gland can be seen through the translucent ceratal wall. Macnae notes that pale specimens are not uncommon.
Macnae named it 'horridus' because it bristles its cerata when 'frightened'. I have never seen the species alive so I can't be sure that pale specimens look like this.

It could also be a specimen of P. hyalinum which is widespread in the Indo-West Pacific or something like P. crypticum which is only known at present from Australia. Although those species look somewhat different, your photo could be of an animal which has lost most of its cerata and is in the process of growing new ones. If it is one of those two species it will probably be associated with colonies of the alcyonariian soft coral Xenia on which they feed.

Best wishes,
Bill Rudman.

Rudman, W.B., 1999 (Dec 6). Comment on Phyllodesmium? from Sth Africa by Valda Fraser. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from