Phyllodesmium hyalinum from South Africa

April 22, 2000
From: Valda Fraser

Dear Bill
I know that Phyllodesmium magnum looks like this, but the size is wrong? This nudibranch is much smaller.  I hope you will have some ideas.  Also, I would like you to comment on the colour variation.  Thanks.
Locality:  South coast KwaZulu-Natal SOUTH AFRICA  near Port Shepstone - 18m
Date:  April 1999
Size:  UPPER: 35mm
LOWER: 26mm
Valda Fraser

Fraser, V., 2000 (Apr 22) Phyllodesmium hyalinum from South Africa. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Valda,
I think this is Phyllodesmium hyalinum. You can see through the almost transparent ceratal wall, that branches of the digestive gland radiate out from a central duct. This cuts out P. horridum which has a simple unbranched digestive gland duct. To confirm this identification I would need a specimen, or at least I would need to know where the anus is, which is difficult to see in living animals because of the cerata. If it is P. hyalinum it feeds on Xenia or a close relative, often hiding in a cavity it eats out in the basal 'stalk' or 'trunk' of the soft coral colony.

Concerning colour. I suspect the paler upper animal is paler in colour because it has a sparser network of digestive gland branches. This could be a result of food shortage. Certainly some aeolids I have looked at resorb their body organs, or parts of them when they are starved.

In some species, such as Phyllodesmium serratum, colour depends on the colour of their food, which itself ranges from white to red, orange and pink. On the other hand some species, such as P. hyalinum feed on only one prey and show little variation. In this case from pale watery white to a creamy brown.

Best wishes,
Bill Rudman.

Rudman, W.B., 2000 (Apr 22). Comment on Phyllodesmium hyalinum from South Africa by Valda Fraser. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

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