Phyllidia carlsonhoffi from Palau and Yap, FSM

Dear Binyamin,

Thanks for these interesting shots. It's not easy to distinguish P. carlsonhoffi and P. madangensis from the dorsal surface so when I saw your upper photo I was pleased to see the characteristic small tubercles alternating with the big tubercles, which is one character of P. carlsonhoffi separating it from P. madangensis according to Brunckhorst. Unfortunately the second animal has only one or two of these small tubercles. However P. madangensis is said to also have a small tubercle in front of each rhinophore and to have the large tubercles more sparsely spaced than P. carlsonhoffi so I think we can say your animals are both P. carlsonhoffi as you have identified them. One apparently good difference is that in P. carlsonhoffi there is a black median line on the sole of the foot which is absent in P. madangensis.

Another interesting point is that your animals are on an orange sponge. We have a growing number of photos on the Forum of phyllidiids on similar orange sponges. Brunckhorst records a number of species feeding on orange sponges of the order Axinellida, so although I can't identify the sponges from the photos, if we continue to get more records of these animals on similar sponges, it would certainly suggest that it would be a useful research project to investigate feeding specificity in the phyllidiids

Best wishes,
Bill Rudman