Still need to know the water parameters. Test ammonia, nitirte, nitrate, pH, SG
, calcium, and alkalinity. These are the basic tests for reef. Please post results. Numbers please.
The coral that hasn't opened yet are a type of polyp. Most likely star polyps of some color variation. It's not dead. It's just tucked in until water conditions are right for it.
It's also important to know the lighting system. Please describe to us what you have. What type bulbs? How many watts?
That slug looking thing is the featherworm's body. The feather part is it's head. The body is no good. The head may anchor and rebuild itself. Testing water parameters will help determine if water quality is an issue.
How long has the tank been up and running with fish in it?
What kind of filter is on the tank?
We, as a people, know so much more about outer space than we do about our own oceans. This lack of knowledge can very well spell the dangers that lay in wait for us.
The oceans surely would swallow us before a rock comes down to smite the planet of it's life.