Phyllodesmium hyalinum from South Africa

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.