After reading your question, and if coral are the invertebrates your are wanting to learn about I would suggest Eric Borneman's Aquarium corals. The other book the others have listed is one I am not familiar with. I MUST have it
One can never be armed with too much information. I would also get more than just one book to get possible different points of view.
Two more books that I refer to many times are Corals a quick reference guide and Iinvertebratesa quick reference guide, both by Julian Sprung. These are both awesome book.