Phestilla melanobrachia Berg 1784

coral polyp phestilla

 

The coral polyp phestilla, Phestilla melanobrachia, has two colour forms, the bright orange one shown here and, as the name suggests, a black form. The name also refers to the gills as arms, rather than giils. The name is sometimes mis-spelled as melanobranchia.
It feeds on coral, which can be seen on the left of the picture.