starfish ID

[Dearth]

Sorry for picture quality but only managed to get one picture before it disappeared found this on tank wall for comparison the snail beside it is one inch long its either grey or brown with black banding long legs small body I have never seen it before and nothing new has been added in 6 months and this is the first time I've seen it.

Seeing as it has not damaged my coral or existing snails and crab I am assuming it is not harmful to either and I am thinking it is a species of brittle star should I leave in tank or try to root it out?