Holthui's Anemone Shrimp (Ancylomenes holthuisi)

Tanjung Paudean, Lembeh. Although my first focus was on the shirmps now I deeply regret not to have made a full pic of the organism they were on. I did not see one like this again in the whole time I was in Lembeh and I now would like to know what it is: anemone, soft coral?? blackish colored...very unique!