the blue linckia is a beautiful starfish but Idk about being well suited for a 55 as they can get to a 1' were the tile/marble gets 5" but the red fromia is another good option as it gets to be 6"
Are any starfish really "well suited" to the average reef tank? Most (if not all) have unknown or specific/limited food requirements. This essentially makes them temporary novelties at best. The only "starfish" I have ever seen last for years (which should be the minimum time frame to consider any sort of success) in a reef are the brittle stars which make excellent scavengers.
I get that they are charming creatures but encourage everyone to help reduce the demand for them commercially.