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Regarding the similarity between Heliofungia actiniformis and Euphyllia glabrescens, I have discussed my opinions previously (Sprung, 1999a and b). I originally came to believe that Heliofungia was more closely related to Euphyllia spp. than Fungia spp. on the basis of the manner in which it often dies and its asexual means of reproduction (Sprung, 1999b). Heliofungia often succumbs to protozoan infections (Helicostoma nonatum) that produce “brown jelly” with necrotic tissue, exactly the kind of infections that affect Euphyllia spp. In Euphyllia these infections can be stopped with a simple freshwater bath followed by careful siphoning off of the necrotic tissue. Euphyllia colonies are composed of series of polyps or separate polyps in phacelloid colonies. If they get an infection it is possible to sever the affected area and save the colony. The result is the loss of one or more polyps (or regions with an oral center) in a colony, but the rest of the colony can be saved. In Heliofungia the “colony” cannot be saved because it is a single polyp. Infections in Heliofungia are almost always fatal. Herein lies a difference with Fungia spp. Fungia spp. are also single polyps, but they can survive loss of some or even most of their tissue mass. In such situations Fungiid corals commonly develop polyp buds called anthocauli on their oral surface, and these buds develop into new fungiid corals that grow and detach from the original “mother” polyp’s skeleton. This mode of reproduction may be possible for Heliofungia under the right conditions, as it is known for many genera of corals, but I have not personally seen it in Heliofungia in an aquarium or in the natural habitat. By contrast, the formation of anthocauli in Fungia spp. is ubiquitous in the wild and in aquaria. Heliofungia actiniformis does form polyp buds, but these are located on the underside of the skeleton, not on the oral surface. This is analogous to the formation of daughter colony buds beneath the polyps in Euphyllia spp.

The assertion that Heliofungia is closely related to Euphyllia is supported further if one looks at the appearance of newly settled polyps of Heliofungia compared to newly settled polyps of Euphyllia glabrescens. They are practically indistinguishable. Both are attached to the substrate. In Heliofungia the polyps break from their attachment point when they reach a certain size, which is the same mode of development that fungiid corals have. It is my opinion that Heliofungia has adapted this mode and the free-living lifestyle to take advantage of habitats where a sessile coral would likely be buried. The physical requirements of such a lifestyle promote development of its shape. Thus I am suggesting that the similarity between the shape of the skeleton of Fungia and Heliofungia is a more a matter of convergence than close relationship. If one compares the density of the skeleton in Heliofungia to fungiids and Euphyllia spp., one finds that the density of the Heliofungia skeleton is more like Euphyllia. The shape of septal and costal teeth on Heliofungia is more like Fungiids, but this might be explained by the physical requirements of a free-living coral of this shape; see for example Hoeksema, (1993). The aforementioned trait of developing bifurcated tentacle tips seems to be another connection to Euphyllia. Note the photographed specimen, which looks like Euphyllia divisa.

Given the choice of revising its taxonomy, one could place Heliofungia in the same genus as Euphyllia. Alternatively it could retain its name and be moved to the family that contains Euphyllia, the recently created family Euphyllidae (Veron, 2001). The latter option seems appropriate to me, if my hypothesis is correct.

As a side note, while I'm discussing taxonomical revisions in the family Euphyllidae, there is another popular reef aquarium coral that I believe is related to Heliofungia and Euphyllia, though its present taxonomy suggests otherwise to the extreme. The coral Galaxea is presently classified with Oculina in the family Oculinidae. Galaxea has absolutely nothing in common with Oculina, a coral that has a dense skeleton and polyp structure clearly like Solenastrea, Astrangia, and the fossil coral Septastrea. The coral Physogyra, which belongs to the Euphyllidae, has a similar skeletal structure to Galaxea, though the polyps in Physogyra are meandroid. The calyces of Physogyra lichtensteini are embedded in a very porous skeletal matrix called coenosteum, as are the calyces in most Galaxea, except for G. (=Acrhelia) horrescens, The living polyps of Galaxea bear no resemblance to those of Oculina, but are very much like tiny Euphyllia glabrescens. See the photo of them side by side for comparison. Looks can be deceiving, so this similarity does not necessarily mean they are closely related as I am suggesting. I hope to have the opportunity to test this hypothesis some day. The similarity goes beyond looks. Anyone who has kept Galaxea is familiar with its stinging abilities and the formation of very long sweeper tentacles. These traits are found in Euphyllia spp., but not in Oculina.

Husbandry requirements for Heliofungia

Lighting

Heliofungia is not very demanding with regard to illumination. It can be kept under standard output fluorescent lights as easily as under high output tubes or metal halide lamps. If it has room to move around, it will choose a location where the lighting is best.

Water motion

Heliofungia does not like very strong water currents. Under strong flow it will not expand fully. It will expand beautifully under slight to moderate water flow that gently moves the tentacles. This movement promotes gas exchange and assures uniform illumination of the whole polyp.

Temperature