Warning: the following is a nerdgasm of coral taxonomy, guest-written by Joe Rowlett, one of the many talented fish geeks working the fish tanks at Old Town Aquarium in Chicago.

Historically, corals have often been grouped at the genus and family level based on morphological structures of the entire colony—for instance, whether a new polyp grows from inside (e.g. Favia) or outside (e.g. Favites) of the old polyp… or if the polyps are grouped together (e.g. Platygyra) or separate (e.g. Caulastrea). These morphological characters had the advantage of being easy to observe, but have now been shown to be misleading when it comes to the true evolutionary history of the stony corals.

When coral researchers began using molecular data to look at coral evolution their results were completely at odds with the classification that had been used for decades. This has required a complete rewrite of our understanding of the coral tree of life, with numerous species, genera, and families being redescribed and renamed. The process is still ongoing, and it will likely be a decade or more before things settle and a new stable classification appears.

With this new framework of species’ relationships, researchers have now been able to more closely look for the more meaningful morphological traits that they had previously missed. What they have found is that the minute details of how the skeleton is secreted— the orientation of microscopic skeletal spines, the derivation of the polyp’s skeletal wall, etc. etc. etc.—is what matters most.

What this means to the average aquarist is that the scientific names we use for corals are now outdated and inaccurate. In the aquarium industry it often takes years for taxonomic changes to become accepted and commonplace amongst retailers, wholesalers, hobbyists, and publications. Hopefully this article will help raise the industry’s awareness for what’s to come.

As this topic is a bit overwhelming when taken in its entirety, I’ll be focusing on the former Suborder Faviina, which includes common aquarium species like: brains, acans, scolys, chalices, blastos. Basically, most large-polyped stony corals (LPS). One major finding has been the importance of biogeography for classifying this group of corals, with Atlantic brain corals now placed in the Family Mussidae, and Indo-Pacific species in the Families Merulinidae and Lobophyllidae.

This has important implications for formerly circumtropical genera like Favia and Montastrea, as new names had to be made for these unrelated Indo-Pacific species. Dipsastrea is now the correct name for Indo-Pacific “Favia”; Phymastrea is correct for the Indo-Pacific “Montastrea”. The former “Montastrea” has so far been split into three genera, with a fourth likely to come when more research is completed.

A similar change has taken place for Scolymia, with the three Atlantic species retaining that name. The former “Scolymia australis” is now Homophyllia australis. The former “Scolymia vitiensis” is now Parascolymia vitiensis. And for good measure, it was determined that “Indophyllia” wasn’t really different enough from Cynarina to warrant its own genus, so it is now Cynarina macassarensis. (This last change is something we as aquarists new all along. Those two were always difficult to tell apart!) And “Acanthophyllia desheyesiana” is once again treated as just a variant of Cynarina lacrymalis.

Phew! That’s a lot of changes. How about some more…

In a brand new article by Arrigoni, et al. “Acanthastrea bowerbanki” and “A. hillae” were shown to belong to their own independent—and as yet unnamed—genus. The same is true for the often-misidentified (and never collected for aquariums!!!) “Acanthastrea maxima”. Furthermore, A. faviaformis was shown to not only not be an Acanthastrea, but it in fact belongs to an entirely different family of coral, Merulinidae. These are the kinds of major changes to classification that are becoming commonplace.

The species name “faviaformis” indicates that it resembles the genus “Favia”, and it turns out this resemblance is due to the fact that it is a “Favia”, or rather Dipsastrea. One final change is to the uncommonly seen A. ishigakiensis, which will eventually be renamed as a Lobophyllia. With all the changes to this genus, it’s unfortunate that they have yet to study the common A. lordhowensis. I think we’d all be a little heartbroken if that most iconic of “acans” turned out to not actually be one.

Chalice corals of the genera Echinophyllia and were shown to need further revision, as the two species of Oxypora examined have each independently evolved from within Echinophyllia. The result of this is that Oxypora will either end up being renamed as Echinophyllia, or certain species of each genus will change names. (This is, once again, a result most aquarists have long recognized. It can be damn difficult trying to identify these chalices to genus.)

Lobophyllia and Symphyllia are two genera that are commonly confused by aquarists. And, as it turns out, this is because Symphyllia are derived from Lobophyllia and will likely have to be renamed as such. [For those uninitiated with the nuances of classification, it is generally verboten to treat a group as separate if it is directly derived from another group. This is termed ‘Paraphyly’. Modern classifications do their best to eliminate these artificial groups, but there are still notable exceptions.For instance: the equal rank of birds, mammals, and reptiles in most classifications, when birds and mammals clearly evolved from reptiles.

But such discussions are neither here nor there for the topic at hand…] It also turns out that the recently renamed Parascolymia vitiensis is deeply nestled in this group and will have to be renamed, presumably as “Lobophyllia vitiensis”. But this awaits a formal revision of the group, which will likely take a few more years. So enjoy saying Parascolymia while you still can.

At a certain point the complexity and enormity of these changes gets to be overwhelming. Have I mentioned that Goniastrea and Favites will likely each be split up into new genera? Or that there is likely to be a third fourth Blastomussa species—the soon-to-be-former Parasimplastrea omanensis is so genetically similar to Blastomussa merletti that it is virtually indistinguishable, in spite of their differing morphology. And this is just one group of corals we are discussing!

The scope of what is being accomplished in rewriting the coral tree of life is truly impressive and unprecedented in zoological taxonomy. With this new information hidden away amongst obscure scientific journals, it is up to us as aquarists to stay informed and up-to-date on these continuing changes. Cheers.