Jim, this was just my personal observation and experience. I disagree; the bristleworms in my system are far more populated in the sandbed under rocks than they are on the rockwork itself. I had 2 healthy clams in the sandbed with bristleworms underneath them just as Larry described. I never thought much of the bristleworms and would observe them come from under the clams at feeding time. I started noticing that their mantles were not extending as much as they could as well as a decline in the hippopus. I lifted both him and my derasa up to a rock ledge, but it was too late for the hippopus. The derasa has since shown exceptional growth and there are almost no bristleworms on the rockwork now thanks to the purple pseudo.