Very first live rock I bought (from florida) back in the mid '80's brought with it a pair of large bristleworms. One was 18" long and as wide around as my index finger. The other was closer to 24" and as wide as my thumb.
Both were model tank citizens and did an absolutely incredible job keeping the crushed coral I was using (complete with UG filter) clean. Remarkable animals, and I've always been disappointed that I haven't found any anywhere near their size since.