(This article originally appeared in the “The Reefer” column in the April 2005 issue of Tropical Fish Hobbyist Magazine, www.tfhmagazine.com)
Amongst all the different corals and their kin that you can keep in reef aquariums, the corallimorpharians can certainly be some of the most colorful, and hardiest, too. They also have the longest taxonomic name I think, so people usually just call them mushrooms anemones. However, while many of them do look very similar to anemones at first glance, they aren't anemones at all, and they actually look more like a stony coral on the inside. But, they aren't stony corals either, which is why they've been given the name corallimorphs. The term literally means "coral shaped".
However, many of them do indeed look mushroom-ish, too, and even though it's wrong - mushroom anemone is still the most common label hobbyists use. They are also called disc anemones or false corals at times, and mushroom corals is used, too. So many names! It seems that the name mushroom corals is being used more and more though, and I'll be sticking with that one, as well.
Regardless of what you want to call them, mushroom corals are indeed close cousins of both the corals and the anemones. In addition, most of them also have symbiotic relationships with zooxanthellae algae, like reef corals and anemones do, as well. So, they are dependent on lighting to some degree, just as most corals and anemones are. However, they don't require as much light as many of their kin, and are easier to please. In fact, most can actually thrive in settings that would be considered way too dark for their other symbiotic relatives.
With that said, even the symbiotic mushroom corals can acquire nutrients in various ways that have nothing to do with zooxanthellae. All of them can absorb nutrients directly from the surrounding seawater, and many will trap particulate matter, bacteria, plankton, etc. in mucous that coats their discs (tops), as well. The food-laden mucous is then carried to the mouth by cilia and eaten. Still others have the ability to capture prey animals as big as small fishes, really being a lot like anemones.
Okay, enough biology for here. Now I'll give you some more details about the four most popular genera, Discosoma, Ricordea, Rhodactis, and Amplexidiscus. Let's take a look at the common corallimorpharians you‘ll find at the store and how to care for them.
Genus Discosoma (synonymous with Actinodiscus):
Members of this genus are considered to be the "common" mushroom corals, and these are sorts that look the most like real mushrooms. They usually have a short stalk that is topped by a flattened disc, which is most often rounded in shape. Sometimes the upper portion may be ruffled, too. Typically growing to a couple of inches or so in diameter, bigger ones can make it to over 3 inches, as well.
The majority of these have relatively smooth discs, but then there are some that have various fine textures and some that are covered by small pimple-like bumps. They can also come in a very broad range of colors from red all the way over to violet, and are frequently striped, speckled, spotted, and/or mottled, too. They can really come in a lot of looks! On top of all that, you may come across some from time to time that are rather fluorescent, and will look especially great with some blue/actinic lighting overhead.
You might find an occasional individual living away from other common mushrooms, but the vast majority of the time they are found living in groups on pieces of rock, sometimes being large enough and spaced close enough together to completely cover the rock they are on. Another thing to mention is that various sorts don't bother each other, so it's not uncommon to find two or more different-looking individuals or groups right up next to each other, or even mixed together on the same rock.
As far as common names go for the common mushrooms, there are a lot. In general, their appearance is simply described in a word or two, and then this is put in front of the word mushroom. Blue pimpled mushroom, green striped mushroom, red mottled mushroom, etc.
When it comes to aquarium care, there's not much to it for these. They can live under moderately bright lighting, or in relatively dark lighting that would be considered unacceptable for corals. Anything in between is fine, but they don't seem to like being under really intense lighting, like metal halides. Do note that if you want to put them under brighter lights, they will need some time to slowly adapt. So, try a dimmer area and slowly move them to a brighter area over a few weeks' time.
Sometimes these can be seen living peacefully around the bases of big leather corals. However, many times they may irritate or even harm many other things they come into contact with. Conversely, they can sometimes be stung by other more aggressive corals and such. So pay attention. Really, even though they often prove to be rather benign, you'll be better off to just avoid putting them somewhere that they can contact other things in the first place, with the exception of other mushrooms.
As long as lighting and aggression are considered, they can also be placed anywhere that the current isn't so strong that it folds them over. Low current areas are best, but a moderate current might be tolerated as long as it isn't always moving in one direction and blowing them over.
These guys only have a little bump for a mouth and don't have any feeding tentacles, making it obvious that they aren't big eaters. Few if any will take any sort of food you might try to hand deliver. Instead, they live off food provided by their zooxanthellae (even in low light), and by trapping tiny food particles in mucous coatings they produce over their discs. They can absorb dissolved organic nutrients directly from the water, as well. Thus, you don't have to do anything for them. However, they still may benefit from the additions of some plankton-type foods and/or the use of a deep sand bed set-up that provides various sizes and types of natural foods.
Lastly, a word about reproduction. Under optimal conditions in aquariums, these can reproduce asexually by fission, meaning they can split themselves in two to make more of themselves over and over. And, they can also reproduce via pedal laceration ("foot cutting") by simply creeping across a surface very slowly and leaving little pieces of their bases behind. Each piece will grow into a new mushroom.
Members of this genus are typically called by the genus name itself - ricordea mushrooms. They are about the same size as the common mushrooms, or a bit larger, but they look quite different due to the numerous tentacles they possess. The disc of a ricordea mushroom is completely covered by short bulb and/or finger-like tentacles that make them look just like baby carpet anemones. These are smooth and rounded in shape, and are quite distinct, so you shouldn't be getting ricordea confused with anything else (unless you think it's a baby carpet anemone, of course).
These also come in various colors, typically being brownish to greenish, and much less commonly colors like red, orange, or blue, etc. So, you'll typically see similar, simplistic sorts of names like orange ricordea, green ricordea, etc. Some will also light up brightly under blue/actinic lighting, just like their cousins. And, like common mushrooms, these are typically found living in groups that may completely cover rocks and such.
These can also be kept under a broad range of lighting, from low to higher intensity, although they often don't seem to care for the intensity of a nearby metal halide bulb either. Likewise, they'll also prefer low to moderate currents, as well. Again, being folded over on top of themselves by a strong current is not going to make them happy.
Really, their care requirements and compatibilities are essentially the same as those of the common mushrooms. They can touch each other but shouldn't be put in direct contact with things, and they can be burned by some aggressive corals, too. They can also reproduce in aquariums through fission, and will likely benefit from additions of some plankton-type foods and/or a deep sand bed set-up, as well. However, unlike the common mushrooms, ricordea 'shrooms will usually take a variety of meaty foods if provided in small pieces. Brine shrimp, blood worms, and even flake food may be accepted, and you can try various other things, too.
Now we get to something quite different. While the other mushrooms are called by color/appearance, there are a few distinct members of this genus, so there are a few common names that aren't simply colors. These include the Tonga/bull's-eye mushrooms, and the hairy/metallic mushrooms.
Unlike the other mushrooms, almost all of these are covered by numerous finely-branching tentacles, or oddly-shaped knobby projections. So again, they are easy to distinguish from the others. Many can also get a heck of a lot bigger than common or ricordea mushrooms and can be eager eaters, too. Some will even eat fishes if given the opportunity, as the tentacles can sting and the mushrooms can close up around a victim. More on that in a minute.
The Tonga mushrooms, which are also called bull's-eyes for some reason can come in strong green, blue, purple, and red colors, grow to 2 or maybe 3 inches across, and are covered by small tentacles. These tentacles are relatively tiny, but they are also very fancy, nonetheless, having lots of little projections/branches.
The others are called hairy mushrooms due to their thick covering of branching tentacles and odd-shaped protrusions (although fuzzy would be much better for most of them), and they can grow to over a foot across at times. Sometimes these are also called metallic mushrooms at, I'm guessing because many can take on an iridescent look under blue/actinic light. They come in several colorations, typically having brown, cream, blue, and/or pink highlights over fluorescent green, too.
Yet again, these can be kept under a broad range of lighting, from low to high intensity, but will prefer low to moderate, and will also prefer lower currents, being unhappy in anything that you'd call strong. They are more aggressive as a whole, though, as many can burn other corals they come into contact with through the production of toxic compounds, while those that have larger tentacles may also use them to sting corals, as well. Conversely, depending on what they come up against, they may also be injured by the stings of more powerful corals though. Keep this in mind when you decide where you want to place them, as the hairy mushrooms are going to get big and need a lot of space if you take good care of them. They will also reproduce under good conditions, via the same means as the others.
These are a bit different when it comes to feeding, too, as most will take small meaty foods if offered. This is especially true for the hairy mushrooms that have larger, more complex tentacles. These are particularly interesting to watch as they will close up around food items like a drawstring bag, slowly engulfing whatever they can fit in their mouths. This can include live fishes if they happen to be small and very slow, or dead.
Conversely, those that have only the fancy rough bumps for tentacles , like the Tonga mushrooms, may only take very small bits of food on occasion, or may take nothing at all. They just don't have the same appetite as the rest. Regardless, all of these will likely benefit from additions of some plankton-type foods and/or a deep sand bed set-up.
Lastly we get to the genus Amplexidiscus, which has only one member. These are called elephant ear mushrooms due to their large size, and they’re all Amplexidiscus fenestrafer. How big is large? While they may stop growing at a little under a foot across, some may keep on going until they’re more like a foot and a half in diameter. That’s a big mushroom.
Elephant ear mushrooms are typically brown to greenish in color and they have a broad but short base. They also have lots of tentacles on their discs, but these are again unique. Their tentacles are often relatively long for a mushroom and are very simple and thin, often ending in a point. They really look a lot more like a big flattened out sea anemone than anything else. Easy to tell apart from the others.
As you might guess, these can also thrive under a broad range of lighting, from low to high intensity, and will also prefer lower currents. Thus, they can also be placed practically anywhere the current isn't too strong. However, these can apparently produce a sort of toxic mucous which can affect corals it comes into contact with, so I suggest you keep them from even coming really close to other things. Again, keep in mind how big they get, as well.
These can also reproduce asexually in aquariums, but unlike the others they don't tend to form big clusters. Instead of splitting or spreading around pieces of themselves over and over, these tend to live a solitary life, or form only smaller groups. Typically, there will be less than a half-dozen in any given spot.
Lastly, these are big eaters, indeed, that can also eat fishes. So beware, as these can and will get hold of fishes you don't want eaten on occasion. You'll need to give them some meaty foods to keep them happy, which can include small fishes if you like. Really, because these are so big and are able to eat smaller fishes, they aren't very popular with most hobbyists for good reason.
Well, that's it for the common corallimorpharians. Sooner or later you might come across something I haven't mentioned here, as there are a handful of Discosoma species that do have tentacles and look more like Rhodactis, and at least one Rhodactis species that doesn't have tentacles and looks more like Discosoma. But, these oddballs are relatively rare in the hobby compared to what we've been over. You may not even see an elephant ear more than a handful of times, depending on where you shop.
References/Good sources for more information:
Borneman, E. H. 2001. Aquarium Corals - Selection, Husbandry, and Natural History. T.F.H. Publications, Neptune City, NJ. 464 pp.
Fatherree, J. W. 2004. The Super Simple Guide to Corals. T.F.H. Publications, Neptune City, NJ. 134 pp.
Fossa, S. and A. Nilsen. 1998. The Modern Coral Reef Aquarium, Volume 2. Birgit Schmettkamp Velag, Bornheim, Germany. 479 pp.