Phyllodesmium hyalinum from the Red Sea

Dear Oren,
I am pretty sure this Phyllodesmium hyalinum, which was described from the Red Sea in 1831. It feeds on the soft coral Xenia and is usually very difficult to find because it burrows into the fleshy 'trunk' of the colony only emerging to feed. In the photo on the left a bit of a Xenia colony can be seen at the top of the photo. It is very similar in appearance to Phyllodesmium crypticum which also feeds on Xenia. Both animals rapidly drop off many of their cerata when disturbed [see autotomy Fact Sheet], and I suspect your animal has lost quite a few of its cerata..

In the photo on the left above, I have ringed the anal papilla. In P. hyalinum it is situated above and slightly behind the second ceratal arch on the right side, while in P. crypticum it is inside the second arch. It is not clear in your photo because many of the cerata are missing, but it is certainly higher than I have seen in P. crypticum. Another difference is that the anterior foot corners in P. crypticum are developed into tentacular processes while in P. hyalinum they form only slightly rounded extensions. In the lower right photo above I have included an inset showing the front of the foot, which looks much more like P. hyalinum than P. crypticum, so my best guess is that this is P. hyalinum.

Best wishes,
Bill Rudman