I have lots of books and truly enjoy understanding what makes a specific species that species. Before I went into the arts, I studied marine biology and botany....and still do some 30 years later.
A word of warning with IDs, they are not really accurate until one can actually examine the skeleton of an adult colony. Many species are still disputed and there are ample examples of incorrectly illustrated species on the web. We still know very little about corals and their variability. I like J.E.N. Veron's theories on reticulate evolution, whereby all species are in constant flux and actively evolving. Deciding where one starts and ends will be a debate without a final answer. We will always find new levels of exactness that allow us to look deeper into the evolution of living things. I suspect, at some point in the not too distant future, people will be counting atoms on a DNA molecule to determine some fine difference. In the end, as Shakespeare once said, ' a rose by any other name would smell as sweet'.