hi
if i were you, i would avoid these at all costs!
they are cold water nems from british waters.
i know, i had some with a setup that i bought, they wont directly harm your corals BUT what they will do is rot away, in usually very hard to get to places, mess up your water and cause you the biggest ever amount of grief possible! ( i know that too)
i had to strip the tank down to get them all out ( wasn`t pleasant)
so unless you are indeed keeping a cold water setup, then for your sake avoid them!