I think that is a red linkia starfish. If it is, they won't really take foods but you can try a small piece of clam. They cruise around and eat bio films. Again, your tank may be too new for that starfish to find enough food.
You can also try to feed the tubeworms but they normally eat tiny particles 24 hours a day. In the sea they do fine, but if you tried to feed them like that in a tank, you would screw up your water. Those two creatures are not really able to survive in your tank for long. You will be better with crabs and shrimp as they eat much larger foods and you can target feed them.
You could get a small arrow crab, they are cool and you can feed it small meaty things. They are easy to care for and comparatively safe in your tank with what you have.