I have had a mantis in my tank since i started it 3 yrs ago.
. never been able to get rid of it.. I also have a smaller reef tank that had several (green)brittle stars in it. Well the brittle stars were getting too big for the smaller tank, they were about 12" to 15" stretched out, so a caught them and transferred them to my bigger fowlr tank(tangs etc.) Since then I havent heard or seen any sign of the mantis..(good thing) The mantis was about 2" long and I think it was a smasher because i would always see small hermit and snail shells with holes in them empty.. Anyway Is it possilbe that these starfish either scared it or have they erraticated the beast....Hopefully.