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Mushroom Corals

What makes mushroom corals the most popular of all soft corals.

By Bob Goemans

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mushroom coral
Mushroom coral.

Their common names include mushroom coral, elephant ear coral, false coral, disk anemone, mushroom anemone and are often linked to their coloration (e.g., green striped mushroom anemone). They are not true anemones, nor are they true corals. They are somewhere in between or, more appropriately, a comparative anatomy or a morph (although more closely related to scleractinian corals). Mushroom corals are found worldwide and most occur in shallow tropical waters.

These photosynthetic animals are probably the easiest of all corals to maintain, as most do better in nutrient-rich surroundings with low to moderate light. And with various sized and colored disc-shaped polyps, they are extremely popular with most aquarists.

Return to Order
The taxonomy information that has existed on this group of organisms has, for a long time, been confusing. Because I am not a scientist and not interested in their DNA or RNA, I have in the past accepted longstanding thoughts as to their classifications. However, recent (2003) revisions by Dr. Vincent Hargreaves have resulted in a new rearrangement of this order. It now encompasses three families (Corallimorphidae, Discosomatidae and Ricordeidae) containing nine genera with 59 species.

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 has been the elimination of the family names Actinodiscidae and Sideractidae. Another, among others, has been that the two genera Nectactis and Sideractis, each with a single species, has now been placed within the family Corallimorphidae. Dr. Hargreaves revisions encompassed two of the three families, with Dr. Daphne Fautin of the University of Kansas working on the third family, Corallimorphidae, which contain the genera Corallimorphus, Corynactis, Nectactis, Pseudocorynactis and Sideractis. Furthermore, the widely used word “Actinodiscus,” which has been used in various aquarium magazine articles for many years, is not a valid term or name anymore.

Asexual and Sexual Reproduction
Propagation in the wild takes several forms and the various asexual methods are the most common. 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. Longitudinal fission is another form of multiplication and occurs when the specimen splits in half. It usually begins at the central orifice or mouth and extends across the whole surface of the disc. Another natural form of propagation is pedal or basal laceration, which are probably the most common in both the wild and aquaria. As the specimen moves over the substrate it leaves a small portion of itself attached to the substrate, which grows into a new clone of the original specimen.

Sexual reproduction also occurs when the larger female polyps, usually centrally located in the groups of some species, release eggs and are fertilized by the smaller male polyps along the outer margins of the colony. Larvae, generally produced in the May to September time frame, then crawl away from the clusters and spread to other areas.

All these forms of propagation can also occur in aquaria, except that hybrids are not able to sexually reproduce as they do not contain functional gonads (V. Hargreaves, 2005).

But if these natural methods are happening too slowly for hobbyists, they can simply cut the entire head off the polyp stalk and then cut it (i.e., the polyp disc) into pie-shaped pieces. The pieces can be placed in a shallow tray of course-grained sand where the individual pieces will attach to substrate particles and form new polyps. The cut stalk will regain its original shape, and in the coming months it will be no different than it was before the cutting.

A loose mushroom/polyp containing at least one sand grain attached to its backside can be glued with underwater glue to a rock or an aquarium side panel. I’ve lined the side panels of some of my aquariums with various colored mushroom corals in this fashion.

Food/Coloring
Depending upon where various mushroom coral 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 area, have periodically appeared on the market.

Because all contain zooxanthellae, they can produce the majority of their own foodstuffs via photosynthesis. However, some also absorb nutrients from the surrounding water and can also trap various substances and bacteria in their mucus coating where it is then moved via cilia to the central mouth area. Therefore, most do not have to be hand fed, yet iodine additives appear somewhat beneficial.

Mushroom Taxonomic Tree

Phylum: Cnidaria (Soft Corals)

Order: Corallimorpharia

Family: Corallimorphidae
Genera: Corallimorphus,      Corynactis, Nectactis,      Pseudocorynacti, Sideractis

Family: Discosomatidae
Genera: Amplexidiscus, Discosoma, Rhodactis

Family: Ricordeidae
Genus:  Ricordia

Common Mushrooms
The most popular mushrooms are found in the family Discosomatidae, genus Discosoma. There are now nine recognized species, with two others presently under investigation. There are also numerous morphs, making exact identification somewhat difficult for the average hobbyist.

They are considered the “common” mushrooms and form small flattened disc-shaped polyps that perch on the top of a short stalk. The discs are usually smooth or ribbed with occasional small bumps and are generally small, about 1 to 3 inches in diameter.

Found in a variety of colors, the purple or blue Discosoma coerulea and the reddish D. ferrugatus and mottled D. marmorata are among the favorites. Both D. coerulea and D. marmorata hail from East Africa to the Central Indo-Pacific and are found in shallow reef areas and lagoons. Discosoma ferrugatus is found from various areas in the tropical Indo-Pacific and inhabit a variety of different reef areas. In the aquarium, it seems to prefer being located in a vertical position such as on the side of a rock.

Discosoma malaccensae, D. nummiforme, D. punctata and D. striata are from various areas in the Red Sea and throughout the tropical Indo-Pacific region. And the species D. neglecta and D. sanctithomae hail from the tropical west Atlantic Ocean, Caribbean and Florida to the Bahamas.

All of these require moderate lighting and gentle water movement. They appear to utilize their own zooxanthellae to supply the majority of their nutritional needs as they have no tentacles for capturing foodstuffs. 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 throughout the aquarium, possibly ending up in an area out of sight where they may waste away.

Because these corals are mostly nonaggressive, they can live in harmony with many other similar type corals. And with many looking quite “fluorescent” under blue/actinic lighting, they make excellent and colorful additions to most reef aquariums.

Elephant Ear
The other two genera in this family — Amplexidiscus and Rhodactis — contain fewer species of major interest.

Amplexidiscus fenestrafer is the only species in this genus, and it is usually referred to as the elephant ear or giant cup mushroom. It generally gets quite large, up to 12 inches or more in diameter. They are usually solitary creatures, but they may occasionally be found in the wild in small groups and appear to only be capable of asexual reproduction. They have short stinging tentacles that are capable of capturing small fish and invertebrates. It is found in the central Indo-Pacific and inhabits turbid shallow reefs and lagoons receiving little or moderate water movement.

In 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 or onion shape while the tasty morsel is drawn into its central mouth area. This extremely hardy species does best under moderate light such as fluorescent lamps and prefers gentle water movement. However, it is known to be aggressive, so provide sufficient space between it and neighboring corals.

Hairy Mushrooms
There are six species in the Rhodactis genus: R. howesii, R. inchoate (usually a nice purple color), R. indosinensis, R. mussoides, R. rhodostoma and R. viridis. They are often called ‘“hairy mushrooms” (except for R. inchoate, which has bumpy-looking tentacles), because they have a covering of small, often branched tentacles. Rhodactis mussoides may attain 8 inches in diameter or larger, yet others grow no larger than about 4 inches.

They are found mostly from the central Indo-Pacific region 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 popular with reefkeepers.

Keep in mind all Rhodactis species are somewhat aggressive and can damage other corals they touch (except those in their own genus), and that they prefer moderate lighting and water flow, thereby making their placement in aquaria different than mushrooms in the genus Discosoma. And because most have tentacles, they can be fed small pieces of marine flesh if you wish to increase their numbers.

Ricordia
In the family Ricordeidae, the genus Ricordia has two members — R. florida and R. yuma — and both are commonly seen in the trade and are probably the most expensive species in this order.

These family members have bubblelike tentacles and are usually 1 to 3 inches across and have colors that range from dark green to light purple.  Some have outer rings of blue, purple and/or orange, or inner circles of orange. These fairly shallow water members need strong light and swift water movement, which are requirements opposite that of the other members in this order.

Ricordia florida hails from the western Atlantic from southern Florida to Brazil, the Gulf of Mexico and the Caribbean, where they are found high on the reef crests where there is excellent water movement and strong light.

Ricordia yuma is an Indo-Pacific species and is usually found moderately high up on the reefs and on substrate high up in tide pools. I’ve found the tropical Atlantic species to be more colorful. Other differences are minimal, except that the Indo species has an upraised central mouth surrounded by a ring of tentacles. Both species are very aggressive and may injure other corals they touch. Neither requires feeding, as their zooxanthellae provide fully for their nutrition.

Final Thought
Without a doubt, these corallimorpharians are among reef hobbyists’ most popular corals, because they are hardy, colorful, easy to maintain and fairly inexpensive to purchase.

References and Sources
Allen, G.R. and Steene, R. 1999. Indo-Pacific Coral Reef Field Guide. Tropical Reef Research, Upper Paya Lebar Road, Singapore.
Borneman, E. H. 2001. Aquarium Corals - Selection, Husbandry, and Natural History. T.F.H. Publications, Neptune City, NJ. 464 pp.
Fautin, D.G. et al. 2002. “Two New Species of Deep-Water Corallimorpharia (Cnidaria: Anthozoa) from the Northeast Pacific, Corallimorphus denbartogi and C. pilatus.” Pacific Science, Vol. 56 (2): 113-124.
Fossa, S. and A. Nilsen. 1998. The Modern Coral Reef Aquarium. Vol. 2. Birgit Schmettkamp Velag, Bornheim, Germany. 479 pp.
Hargreaves, V.B. 2002. The Complete Book of the Marine Aquarium. Salamander Books Ltd., London.
Hartog, J.C. den. 1980. “Caribbean shallow water Corallimorpharia.” Zoologische Verhandelingen. Leiden 176: 1-83, figs. 1-20, pls. 1-14.
Humann, P. and DeLoach N. 2002a. Reef Creature Identification: Florida, Caribbean, Bahamas. New World Publications, Jacksonville, Florida. Humann, P. and DeLoach N. 2002b. Reef Creature Identification: Florida, Caribbean, Bahamas. 2nd Ed. New World Publications, Jacksonville, Florida.
Sprung, J. and Delbeek, J.C. 1997. The Reef Aquarium. Vol. 2. Ricordia Publishing Inc., Coconut Grove, Florida.

 

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