the large serpents like the orange and green get way to big for a nano may prey on small fish
stars like the chocolate chip are predatory need to be feed, and may cause trouble with inverts
sand sifting stars will starve in a nano as will must sand sifting cukes
urchins eat coraline algae and will bulldose things over
filter feeding cukes rarely make it in small systems
a black brittle star would probably be OK but it will hide under the rock so you won't see much of it and the rock needs to be very stable cause it will dig sand out from under it