This article is a guest post by long term coral-taxonomy Liason Joseph Rowlett. HisIndo-Pacific corals bookis one of the best and newest references to learn more about coral identification.
Coelastreahad a troubled entrance into this world. The genus dates to an 1866 paper by the illustrious Addison Emery Verrill, in which he briefly describesC. tenuisbased on a single specimen collected from the “Sandwich Islands?”. These islands are better known to us today as Hawaii, but, alas, there is no coral in this region resembling Verrill’s specimen; in fact, just a single merulinid occurs there, the decidedly differentCyphastrea ocellina. So, whither the tenuis?
Owing to the confusion surrounding this name,Coelastrea(pronounced seal-ASS-tree-uh) was largely ignored for much of its existence, more often than not being regarded as a synonym ofGoniastrea—both genera possess lobes on the inner margin of the septa, forming a “crown” encircling the columella, a trait that separates these from similar merulinids, such as最爱和Platygyra.
But this changed following a 2014 revision of the merulinids, wherein specimens ofGoniastreaaspera和G. palauensiswere shown to be genetically closer toDipsastraea(a genus comprising the Indo-Pacific species formerly inFavia). Comparison of the type specimens ofC. tenuis和G. Aspera揭示两者可能代表相同的物种,因此Coelastrea从死者中复活,从分类学上讲,尽管很难在形态学上诊断。
Likewise, there is considerable uncertainty regarding how diverse this group is. If we were to assume thatC. tenuis和C. asperaare truly one and the same, then it would seem there are only two members.C. aspera has been recognized as widespread in the Andaman-Pacific region (though it has also been questionably reported from the Western Indian Ocean), and it is by far the more commonly reported species, often occurring in abundance on intertidal reef flats.
The other species,Coelastrea palauensis, is described from Palau and was originally classified withinFavia, due to the type specimen having weakly separated corallite walls (i.e. subcerioid). But since this species more often than not has fused corallite walls (i.e. cerioid), it was later shuffled into最爱. . . and since there is also a prominent crown of septal lobes surrounding the columella, it was ultimately reclassified as aGoniastrea, before finally settling into its current home inCoelastrea. Aquarists will be familiar with this coral as the ‘Prism Favia’ (or, rather, one of the Prism Favias, as this trade name is applied haphazardly to a variety of multi-colored merulinids).
The main morphological distinction with these species is size:C. asperahas corallites that average 4–8 mm in diameter, far smaller than inC. palauensis, whose corallites can reach upwards of 2 cm. Colonies ofC. palauensisare also much smaller, rarely with more than a few dozen polyps, whereasC. asperaforms pillowy colonies with hundreds of polyps. Coloration may also diagnose these to some extent, as the ‘Prism Favia’ tends to have contrastingly colored oral discs and corallite walls, whileC. asperais most often brown or mottled brown.
But of course things are not so simple, dear reader. Reproductive differences have been noted in the population ofC. asperafrom Japan, and this was recently investigated in a study by Mitsuki et al. It has been shown that some colonies emit eggs and sperm separately, while other colonies release bundles of egg and sperm together, with these two groups spawning at different times. Lo and behold, genetic data confirms that these are indeed distinct species, occurring in sympatry throughout much of the West Pacific.
Morphologically, they are nearly indistinguishable, save for some very minor differences in the septal spines. Examination of the type specimens ofC. aspera, C. tenuis,以及其他几个声称的同义词(Equisepta,Mantonae,Spectabilis,cromustans),导致了人们对长期被遗忘的认识C.尖端as a valid species for the bundled-gamete colonies.
The Mitsuki study was exhaustive in their inquiry, utilizing breeding studies to confirm that cross-fertilization of these species is rarely successful. Their distributions are similar, buy slightly different, withC. asperahaving a more limited range, ending abruptly at the Amami-Oshima Islands (thus not extending into the cooler reefs of mainland Japan), whereasC.尖端occurs as far north as Wakayama, and also into the Andaman Sea, whereC. aspera显然不存在。
Our old friend Addison Emery Verrill describedGoniastreaaspera(in fact, it was published in the very same paper, on the very same page, describing the presumably conspecificC. tenuis),他设法让造成混乱gins of this species as well. His description quite clearly states that the type locality was Hong Kong, but the specimens themselves bear labels indicating their provenance was “Loo Choo”, thus somewhere in or around Okinawa. Nice work, Addison.
And somehow this genus gets even more confusing! There’s genetic data suggesting the presence of another nearly indistinguishable species, with specimens found in Saudi Arabia, Thailand, and Japan—the single specimen examined from Japan had green oral discs, while the Arabian material has been tentatively identified as bothC. aspera和C. palauensis, suggesting some level of phenotypic plasticity.
And there’s also some concern surrounding another species described by the loathsome Addison Emery Verrill; his FijianPrionastraea spectabilisis a poor match for anything in Coelastrea. And it’s also quite possible that the specimens genetically sequenced for the Huang et al revision were misidentified, calling into question whetherC. palauensis正确分类了 - 他们的研究中使用的材料C. aspera和C. palauensisall originated from Singapore, where the ‘Prism Favia’ phenotype appears to be absent. And compounding all of this uncertainty is the reticence of morphologists
like Charles Veron, who brusquely dismisses the Huang et al revision, stating that “[Coelastrea] is a synonym ofPlatygyra”.
So where does this leave us?Coelastrea Tenuisis probablyC. aspera, which isn’tC.尖端, orC. palauensis, which may or may not be misclassified… plus there’s probably another species that needs to be recognized, and maybe alsoC. spectabilis. Merulinid taxonomy is not for the faint of heart. Avoid it at all costs.