Mushroom Corals – The Corallimorpharians
by Bob Goemans
One of the most popular corals, besides being almost indestructible, is the Mushroom Corals. Their common names include Disk Anemones, Mushroom Anemones, Elephant Ear Coral, False Coral and of course, Mushroom Coral. Even though the word ‘anemone’ is used quite frequently in their description, they are not true anemones, nor are they true corals. But are somewhere in between or more appropriately, a comparative anatomy or simply put, a morph (yet more closely related to scleractinian corals).
They are found worldwide with most in shallow tropical waters and because they do better in nutrient rich surroundings and almost all are photosynthetic, they are probably the easiest of all corals to maintain. And with various size and colored disc-shaped polyps they are understandably extremely popular.
The existing taxonomy information on this group of organisms has, for a very long time, been confusing to say the least. In the past I've accepted longstanding thoughts as to their classifications since I’m not a scientist. But that all ended in 2003 when revisions by Dr. Vincent Hargreaves resulted in a new rearrangement of this order. It now encompasses 3 families (Corallimorphidae, Discosomatidae, and Ricordeidae) containing 9 genera with 59 species, and is currently shown below. In fact, Dr. Hargreaves worked with the world’s leading authority in this field, the late Dr. J. C. den Hartog, when beginning this revision. One of the results of this revision has been the elimination of the family names Actinodiscidae and Sideractidae. Another revision has been that the two genera, Nectactis and Sideractis, each with a single species, have now been placed in the family Corallimorphidae. Bear in mind that Dr. Hargreaves revisions encompass two of the three families, and that Dr. Daphne Fautin of the University of Kansas is working on the third family, i.e., Corallimorphidae, which contain the genera Corallimorphus, Corynactis, Nectactis, Pseudocorynactis, and Siderctis. And I should add that the widely used term ‘Actinodiscus,’ which I have seen used in articles for many years, is not really a valid name!
As for those in the family Corallimorphidae, occasionally, species in the Corynactis or Pseudocorynactis genera enter the trade. Neither is well suited for aquarium life. Those in the Corynactis genus are a temperate species, known as Strawberry anemones. They are usually only slightly larger than 1 inch (2.5 cm) in diameter and colonial, reproduce by fission and pedal laceration, and feed on zooplankton and particulate organic matter. The Caribbean/Central Atlantic Pseudocorynactis caribbeorum species is much larger, about 6 inches (15 cm) in diameter, and usually not colonial. It mainly opens its tentacles at night, and closes rapidly when sensing light. It also feeds on zooplankton and particulate organic matter. To keep them healthy and encourage division in aquaria they need to be fed at least several times per week. A "milkshake" of chopped seafood can be used, but they will also take flake or pelletized foods and frozen shrimp or worms as noted by Julian Sprung. Yet in my opinion, they are species better left in the wild
Mushroom corals naturally multiply in various ways and are also quite easy to propagate in aquariums. ‘Budding’ is a term used when a new polyp develops on the stalk. It usually migrates onto adjacent substrate and quickly develops into a clone of the original specimen. There is also ‘Longitudinal Fusion,’ which is another form of multiplication and occurs when the specimen splits in half. Often, it begins at the central orifice/mouth and extends across the whole disc. Another natural form of propagation is called ‘Pedal Laceration’ which occurs when the specimen moves over substrate and leaves a small portion of itself attached to the substrate. This small piece then grows into a new clone of the original specimen.
For those hobbyists that don’t want to wait for nature to takes its course, they can simply cut the entire head off the stalk and then cut it into pie-shaped pieces. Those pieces should then be placed in a shallow tray of course sized sand with gently flowing water across its surface area, where in a few days those individual pieces will attach themselves to the substrate particles and in due time form new polyps. Keep in mind the cut stalk will regain its original shape and in the coming months be no different than it was before the cutting.
In fact, I’ve taken many loose mushrooms containing at least one sand grain attached to its backside and glued the sand grain with the mushroom to some of my aquarium side and back panels, making for a very nice looking effect.
The most common mushrooms are found in the family Discosomatidae, genus Discosoma. There are now 9 recognized species, with 2 others presently under investigation. (Recognized by scientists that is!) Nevertheless, because there are numerous morphs and we aquarists are without the capabilities to resolve DNA/RNA factors, it makes an exact identification of some specimens somewhat difficult to say the least. These mushrooms form small, about 1 to 3 inches (2.5 – 7.5 cm), flattened disc-shaped polyps that perch on top of a short stalk and are usually smooth or ribbed with occasional small bumps.
The purple or blue Discosoma coerulea is one of the favorites, as is the reddish Discosoma ferrugata and the mottled Discosoma marmorata. Both D. coerulea and D. marmorata hail from East Africa to the Central Indo-Pacific Ocean and are found in shallow reef areas and lagoons. D. ferrugatus hails from various areas in the Tropical Indo-Pacific and inhabits a variety of reef areas. In the aquarium, it seems to prefer being located in a vertical position, such as on the side of rock.
Discosoma malaccensae, Discosoma nummiformis, Discosoma punctata, and Discosoma striata hail from various areas from the Red Sea throughout the Tropical Indo-Pacific Ocean. And the species Discosoma neglecta and Discosoma sanctithomae hail from the Tropical West Atlantic Ocean, Caribbean, and Florida to the Bahamas.
All of the above require moderate lighting and gentle water movement, and utilize their zooxanthellae to supply their nutritional needs since they have no tentacles. If they are given too much light or become too crowded, even though they normally live in small groups, they may detach themselves and drift around the aquarium, possibly ending up in an area out of sight where they may waste away. Since they are mostly non-aggressive, they can live in harmony with many other corals. And with most looking quite ‘fluorescent-like’ under the blue/actinic form of lighting, they make excellent additions to most reef aquariums.
The other two genera in this family, Amplexidiscus and Rhodactis contain few species of interest, even though they are commonly seen in the trade.
Amplexidiscus fenestrafer is the only species in this genus, and generally referred to as the Elephant Ear or Giant Cup Mushroom. It gets fairly large, up to 12 inches (25 cm) or somewhat more in diameter. They are generally solitary creatures, however, may occasionally be found in the wild in small groups. They have short stinging tentacles that are capable of capturing small fish and invertebrates. It hails from the Central Indo-Pacific Ocean and inhabits turbid shallow reefs and lagoons receiving little or moderate water movement. In our aquaria, it can occasionally be fed small pieces of fresh fish, clam, or shrimp flesh, which will cause it to slowly close up to form a balloon/onion shape while the tasty morsel is drawn into its central mouth area. Does better under moderate light, such as fluorescent lamps and prefers gentle water movement.
There are 6 species in the Rhodactis genus, i.e., Rhodactis howesii, Rhodactis inchoata (a nice purple variety), Rhodactis indosinensis, Rhodactis mussoides, Rhodactis rhodostoma, and Rhodactis viridis. They are usually called ‘Hairy Mushrooms’ (except for R. inchoate, which has bumpy-looking tentacles) because they generally have a covering of small, often branched tentacles. R. mussoides may attain 8 inches (20 cm) in diameter, yet the others grow no larger than about 4 inches (10 cm). They hail mostly from the Central Indo-Pacific Ocean and are found on reef slopes and in shallows, and sometimes where the nutrient level is more concentrated such as in bays, lagoons, and boat channels. Their colors are usually brown or green, and their low cost and easy maintenance make them very popular with reef keepers. They are, however, somewhat aggressive and prefer moderate lighting and water flow, and can be fed small pieces of fish/shrimp flesh.
In the Family Ricordeidae, the genus Ricordia has 2 members, Ricordia florida, and Ricordia yuma and both are commonly seen in the trade and probably the most expensive in this order! These family members have bubble-like tentacles and are usually 1 to 3 inches (2.5 - 7.5 cm) across and have colors that range from dark green to light purple. Some have outer rings of blue/purple/orange. These are fairly shallow water members needing strong light and swift water movement, which are requirements opposite that of the other members in this order. R. florida hails from the Western Atlantic Ocean, i.e., Southern Florida to Brazil, Gulf of Mexico, and the Caribbean where it is generally found high up on reef crests where excellent water movement and strong light exists. R. yuma is an Indo-Pacific Ocean species and is usually found moderately high up on the reefs and substrates high up in tide pools. I’ve found the Tropical Atlantic species to be more colorful, however other differences are minimal, except with the Indo species having a upraised mouth surrounded by a ring of tentacles. Both species are aggressive and may injure other corals they touch, except for those more aggressive. Neither require feeding, as their zooxanthellae provide fully for their nutrition.
Depending upon where various species are collected their colors may be more or less pronounced. Colors can range from a solid or variations of colors. Red, purple, blue, mauve, and green seem to be the most popular. Even circular patterns, with green around the outer rim and a deep red inner center have periodically appeared on the market.
In closing, all mushrooms contain zooxanthellae, therefore they can produce the majority of their own food via photosynthesis. However, some also absorb nutrients from the surrounding water and/or trap various substances and bacteria in their mucus coating where it is then moved to its central mouth area. Therefore, most do not have to be hand fed, yet iodine additives appear somewhat beneficial. Besides the varieties of colors and textures, their low cost and maintenance requirements make them very popular with most aquarists.