Very hard to tell from the picture. Is it alive or dead? Can you get a couple more pictures of it from different angles?
Almost looks like a clam expelled some type of internal organs or a coral released something that was partially digested. Any missing fish in the past few weeks that a coral might have partially digested?
"Simply put, you believe that things or people make you unhappy, but this is not accurate. You make yourself unhappy." Wayne Dyer