mine are between 2 and 5 inches long, I have 4 large ones in my display and 2 smaller ones in my fuge. None of them have bothered any of my corals (sps, lps, zoas, shrooms, leathers) or my clams and the fish basically ignore them. Mine are breeding in my tank and I have several hundred babies growing in the sump. I think these critters are fascinating. Good luck with your guys!