Someone is snacking on my Sifting Star

Also, not to get off topic to mistreatment of starfish, but there are several hundred species in the Aiptasia SP. Most are considered harmless feeders grabbing particles and their sting is also considered mild compared to the one you are referring to which is the glass aiptasia anemone.
With ALL anemones, they have to be monitored around certain corals due to their potent stinging capabilities. I don't consider my Viatrix globulifera any different from a quadricolor in the way I care for them. They are not the prettiest anemone in the trade but they serve their purpose in the overall picture of my tank.