Brittle star being eaten!



Please help!
I noticed my brittle star has three missing legs today. It has been under the developing live rocks completely content when I noticed its legs here gone. I have a black rock urchin that has been completely fine, its been active and from what I read its an indicator species that something is wrong in the tank when it goes downhill. All my levels are perfect as I just tested yesterday! The salinity is perfect as well as I check that every morning and evening. I have a pair of clowns, a six line wrasse, a firefish goby, 4 yellowtail damselfish and a coral angelfish. I did just see it nip at the brittle star, is that the culprit? It has been in the tank for 2 weeks now with no problems until now. Please help!