Is that a hellfire? Looks a little like
Actinodendron plumosum to me.
Don't know much about them except that you don't want to touch them. They seem to be photosynthetic but still require feeding. I found one page that claims a max size of 12" and that there are reports of these anemones killing fish, so ... I don't know what to suggest re. the cowfish. How big is the cowfish (he's kinda big isn't he, didn't I see a picture recently? Don't remember). So he might be OK, but ... I don't know how to suggest making that call.
Some links
http://nhm.ku.edu/inverts/adorian/actinodendronidae.htm
http://www.saltwaterfish.com/vb/showthread.php?t=192627
http://www.edge-of-reef.com/anemoni/...plumosumen.htm