If you are going to have
any chance at correctly identifying a coral, you will most likely have to have a
skeletal sample of the coral in question. You will also need to become
familiar with the termonology used to describe indentifying features.
The following links go into such details and will be very helpfull to
you if you read these articles.
Taxonomy of Stony Corals
Taxonomy of Stony Corals Part 2
Taxonomy of Corals Part 3
( soft
corals, zooanthids)
Do Note, that most coral species are capable of growing in many
different forms or shapes, all due to what reef conditions they find
themselves in. The taxonomy of stony corals part 2 will show you photo
examples of the many different shapes that corals can form.