The Giant Cup Mushroom is the largest of the mushroom corals, and loves to snack on fish!

The species A. fenestrafer currently is the only imported species from the Amplexidiscus genus. The True Elephant Ear Mushroom or Giant Cup Mushroom has an oral disc with beadlike verrucae that are sparsely spattered across the surface. The name fenestrafer means “windowbearer” in Latin and has to do the bare area near the edges of their oral disc. Once contact with the mushroom is made, its stinging cells immobilize the prey, and then it closes up within 3 seconds.

The Giant Cup Mushroom is great for a predatorial reef with large fish that cannot be consumed by this mushroom. With smaller fish it has a nasty reputation for eating the little guys that venture too close, and ‘little guys’ can be a 6″ fish!

Mimicking the Carpet Anemones (Stoichastic sp.) has proven useful to the Giant Cup Mushroom. Unwary clown fish may think they have found a host. A typical form you will see the A. fenestrafer in is a partially closed cup. Closing almost all the way, they fool a fish into thinking it has found this sweet cave to hide out in, only to have a rude awakening as this purse shape closes quickly around its tasty meal.

The Giant Cup Mushroom is easy to care for. Though typically it grows to 8 – 10 ” (20 – 25 cm), the Amplexidiscus fenestrafer can grow up to 18″ (45 cm) or more. It is not as finicky as other mushroom corals as far as light and water movement, although it does better in moderate light. If they are not doing well in one area of the tank, by changing its location and by extra feedings, it will adjust. For a large reef it is a great addition. It will neatly fill up the space and provide you with an impressive showpiece.

The A. fenestrafer are bred in captivity and they are very easy to propagate in any home aquaria, which can contribute to preserving the wild populations. Just keeping it well fed with small pieces of fish and crustaceans will cause the it to multiply quickly. Even after splitting, the clone mushroom at times doesn’t always resemble the “mother” mushroom. Predators are unknown.

Giant Cup Mushroom, Amplexidiscus fenestrafer, fish eater

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True Elephant Ear, fish eating mushroom

With more than one mushroom coral being referred to as “Elephant Ear,” it can be confusing, however this particular species, Amplexidiscus fenestrafer, will eat your fish. It is easy to tell the difference since they have quite long tentacles and the outer margin is lacking tentacles. They can close up around a fish or invert that dares to venture too close with in 3 seconds, using their tentacles to sting the victim. They do not close fast if the food item is not alive or if they are kept well fed. They have the ability to take down a fish as long as they are! Provide 50 gallons or more.

Scientific name

Family: Discosomatidae
Species: Amplexidiscus fenestrafer

Distribution / Background

Mushroom Coral Information: The Giant Cup Mushroom Amplexidiscus fenestrafer was discovered by Dunn and Hamner in 1980. Some names they are known for are True Elephant Ear Mushroom, Folded Elephant Ear, Giant Mushroom Anemone, Giant Cup Mushroom, Giant Anemone, Hairy Mushroom, Giant Elephant Ear Mushroom, Giant Disc Anemone, Giant Flower Coral, and Mushroom Anemone.

Where Mushroom Corals Are Found: The Amplexidiscus fenestrafer are found in the Tropical Indo-Pacific Ocean. The species A. fenestrafer is currently the only imported species from this genus. The name fenestrafer means “windowbearer” in Latin and has to do the bare area near the edges of their oral disc.

Mushroom Coral Habitat: These True Elephant Ear Mushrooms are found in shallow waters that are anywhere from quiet to turbid, in areas of subtidal coral reef lagoons. They are found alone, and at times in clusters. They like to grow on dead corals in a vertical formation, as well as on rock. They derive nutrition from their symbiotic algae, zooxanthellae, that dwells within their tissues. And yet they commonly feed on fish and crustaceans as well. It is thought that they use a scent to lure prey to themselves. Once contact with the mushroom is made, their stinging cells immobilize their prey, and then within 3 seconds the mushroom closes up. Predators are unknown.


The Amplexidiscus fenestrafer is not on the IUCN Red List for endangered species


What do Mushroom Corals look like: These Coral Mushrooms Amplexidiscus fenestrafer are basically a coral without a skeleton and their internal structures are the same as stony corals. The top of their body or the upper surface is called the oral disc. The stalk area, which is very small, is called the column and it is located just above the pedal disc, which is where they attach to surfaces.

Various colors within their body include brown, ivory, green and greenish gray that fade in color toward the outer edges. At times they will make a balloon-like shape which is thought to be formed when needing nourishment or if the light level is low or low quality due to age. With this shape they have formed, fish will be fooled into taking shelter in that little “cave” only to become a meal for the mushroom. This distinct purse like enclosure that envelopes around the prey can actually hold up to a gallon of water in the larger species.

On the surface, the A. fenestrafer have short feeding tentacles to capture prey that hold several types of stinging cells. These beadlike verrucae are sparsely spattered across the oral disc. When the animal contracts, these will form into short lobed tentacles around the margins of the disc.The distinguishing feature that helps to identify this genus from the Rhodactis or Discosoma genus, is that their outer edge is almost translucent and does not have verrucae. When feeding, the mouth remains closed until the entire oral disc is closed. The mouth then opens and consumes the prey. Then it will close before the oral disc opens up again.

Mushroom Coral Life Cycles: These mushrooms typically grow to 8 – 10 ” (20 – 25 cm), but can grow up to 18″ (45 cm) or more, depending on the species. Their life span is unknown.

Difficulty of Care

Mushroom Coral Care: The Giant Cup Mushroom is easy to care for and is not finicky as far as light and water movement, although it does better in moderate light. If they are not doing well, they can easily be brought back by changing their position in the water and by extra feedings.

Foods / Feeding

Mushroom Coral Feeding: The Giant Cup Mushroom is a carnivore. Like most mushroom corals, they are also well equipped with nutritional alternatives for their well-being. In the wild, they can derive nutrition from their symbiotic algae, zooxanthellae, that dwells within their tissues. Yet these corallimorphs also feed on fish and crustaceans by luring them into their partially closed “purse-string” like enclosures. Seeking what looks like good shelter, once inside, the coral mushroom will just close up and consume their prey. Larger particles are also trapped on the surface when fully open, and consumed in the same manner.

In captivity, although your A. fenestrafer have zooxanthellae to get some of their nourishment, they can be fed pieces of fish and crustacean flesh when smaller and whole thawed fish such as silversides when they grow larger. Keeping them well fed in a tank with fish is a wise idea. They feed at night, so right after lights out, you can easily pop some dinner in their mouth.

Feed as often as they will close up around foods and eat. The more your feed them, the faster they multiply if that is your aim. Interestingly, their feeding response will not happen with any touch, but only the touch of prey, indicating a chemical response is needed, not just any touch like your finger or another object.

Aquarium Care

Water changes of 10% bi-monthly or 20% a month are typical. Provide a reef environment with proper magnesium levels. Some claim proper iodine levels are beneficial also. Due to their toxins, active carbon is a good idea with larger colonies of mushrooms. Do not over skim since the A. fenestrafer need nutrients to survive on and will not do well in a pristine environment.

Aquarium Parameters

A typical live rock/reef environment is what is needed for your Giant Cup Mushroom. Provide rubble or dead coral and live rock for them to have something with which to attach their pedal disc. Strong water movement will also cause them to detach. Corallimorphs can float around when looking for a place to settle, so it’s a good rule of thumb to have all of your pumps covered. Most good quality pumps have guards on them.

  • Minimum Tank Size / Length:50 gallons or more
  • Marine Lighting: Low to high
  • Temperature: 72° – 83° F (22° – 28° C)
  • Salinity / Specific Gravity: 1.023 to 1.025
  • Water Movement: Low / weak to moderately strong
  • Water Region: Bottom of the aquarium

Compatibility and Social Behaviors

The Giant Cup Mushroom is semi-aggressive if they are near another coral. They will cause other corals to loose tissue, recess possibly die. Acroporas will not grow in aquariums with large mushroom populations. Make sure to leave 6 – 8 ” between your mushrooms and other corals. Watch the growth rate since the A. fenestrafer will overgrow and kill any nearby corals. Even being “downstream” will affect other corals since this mushroom will use mucous nets to capture particles as well as fish.

Slow moving fish and shrimp run a risk of being consumed by the A. fenestrafer. At times, clown fish may adopt a Giant Cup Mushroom as a host, however this could be the final decision that clownfish will make

Mushroom Anemones will tolerate their own species and usually other Mushrooms. In the wild many species of Mushroom Corals occur together in large groups. In captivity A. fenestrafer will get along with their own species, but may not tolerate mushroom species outside their colony. Even in one genus, if the color is different or a different species, the weaker mushroom will detach and find another location. Strong water movement will cause them to detach as well.

Sex – Sexual differences

No sexual difference in appearance is known.

Breeding and Reproduction

  • Mushroom Coral Reproduction:
    Corallimorphs reproduce in 4 different ways. The first three ways, asexual budding, laceration, and division/fission, are successful in the aquarium as most hobbyists soon discover. Budding is where individuals are formed from particles divided off from the pedal disc. Similar to budding, laceration happens when they move slowly over the surface and leave behind small pieces that will eventually form into mushrooms. Division or fission is where an individual divides down the center and forms two animals.
    Sexual reproduction is where eggs and sperm are released into the water column. They unite and form free-swimming larvae which are initially plankonic, and them settle and adhere to the substrate. Sexual reproduction has not been well documented, and has not been observed in captivity. Presumably modern filtration methods are inhospitable to free swimming larvae.

  • Mushroom Coral Propagation:
    Mushroom corals can be easily propagated in captivity by cutting individual polyps into several pieces. Placed the pieces on a gravel substrate with low water flow. They will attach themselves to pieces of gravel. Later they can then be super glued to a suitable substrate such as a reef plug. It has been stated that the warmer end of their temperature spectrum encourages reproduction.

For details on how to propagate your mushroom corals see Mushroom Corals: Mushroom Coral Propagation

Potential Problems

The A. fenestrafer are disease resistant, and only affected by improper husbandry. Problems for the most Corallimorphs are pretty minimal unless your lighting, water movement, feeding and water quality are improper for these animals. A sign of this is if your coral mushroom detaches to look for “better conditions” to settle in. They have very few predators if any.


Mushroom Corals for Sale: The Giant Cup Mushroom, Hairy Mushroom, or Elephant Ear Mushroom A. fenestrafer can be found easily online and at pet stores, as well as from frag farmers and most reef clubs. It is usually found under Giant Cup Mushroom and not its scientific name. Online they are $48.00 USD or more depending on the size of the rock they are sold on. Some may sell them individually as well.


Featured Image Credit: chonlasub woravichan, Shutterstock