I disagree with smoyer's advice.
I believe that ORA's "hawkins echinata" is not a true
Acropora echinata. If in fact it is, then the morphology it displays in most closed systems doesn't resemble an
echinata. Regardless, I don't think it is a good coral to use as a reference.
Going by what some online vendor labels their corals is
very unreliable. Other than Live Aquaria, the majority of vendors are responsible for mass mis-identifications. If it looks like a particular species at first glance, hobbyists and vendors are quick to jump to a rash conclusion. If more people were honest, this problem wouldn't be rife throughout the hobby.
In my experience, the most reliable source is Charlie aka John or J.E.N. Veron. He has written an excellent 3 volume reference that has great images (including corallite detail shots which are usually essential to sound
Acropora ID's) and descriptions which can also help highlight the differences between species. To the best of my knowledge, Veron is still the leading authority in this field.
Obviously, not every hobbyist wants to pick up the set. It isn't cheap, but it is a good investment if coral identification interests you. The Australian Institute of Marine Sciences (AIMS) used to have Veron's pages easily accessible online. While the site has some issues, the raw information is still available. Simply google search the scientific name of the species in question followed by "AIMS". For example: "Acropora echinata AIMS" or you can go to their site:
http://www.aims.gov.au/ and input the species name in their search bar (this will yield the relevant pages).
Sometimes there isn't a page for the species, but clicking on the other results and digging around a little will nearly always work. Just like for the
echinata search, after visiting the
A. turaki page one sees that
echinata is a similar species and following the link will bring you to the
echinata page.
With experience, recognizing the subtle differences in corallite structure amongst similar species becomes easier.
I hope this helps. :wave:
Jake