AquaticCare difficulty: IntermediateLegal complexity: Low

Giant elephant ear mushroom

Amplexidiscus fenestrafer · also called Elephant ear anemone, Giant cup mushroom

No known corallimorph grows larger: its disc reaches about 45 cm and can snap shut around prey like a drawstring bag. It is a fish eater. Contact with the disc can set it off, and a fish resting on it overnight may be caught and eaten, so any fish you care about should be kept elsewhere. The trade name is loose, and small pieces labelled elephant ear are usually a far smaller Rhodactis. Keep it clear of corals, because a keeper reported serious sting damage to neighbouring corals.

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Quick facts

Size	Oral disc usually 20-25 cm across and up to about 45 cm, the largest of any known corallimorph; aquarium animals are often described at 30-35 cm (12-14 in).
Lifespan	—
Social needs	solo
Native region	Tropical Indo-Pacific, including the Great Barrier Reef, eastern Indonesia, Palau and Guam
Origin	Old World
Climate	Tropical
Water type	Marine
Family	Discosomidae
Genus	Amplexidiscus

Part of the Mushroom Corals

Soft, disc-shaped corallimorphs (Rhodactis, Discosoma, Ricordea, and bounce morphs) that carpet rockwork in fluorescent colors. Hardy, low-light, low-flow, and among the best beginner reef invertebrates.

Bounce Mushroom Discosoma (Red Mushroom)Rhodactis Mushroom Ricordea mushroom Ricordea Yuma St Thomas mushroom

Habitat & enclosure

Give it moderate light, low to moderate flow and room for a very wide disc, low in the tank or on the bottom. In the wild it lives in fairly shallow, quiet, often turbid water on the lagoon side of reefs, recorded from the Great Barrier Reef, eastern Indonesia, Palau and Guam. It is widely reported at about 5-25 m.

Keep stable reef water: SG about 1.025, 24-27 °C (75-81 °F), pH 8.1-8.4. It tolerates somewhat richer water than many reef animals.

Substrate

Set it on low rock or the bottom in a spot it can keep, as it will not move itself far. Choose the place with care, because an adult is hard to shift.

Equipment & setup

Moderate reef lighting and gentle flow are enough. Plan the tank around the size of the disc, and allow at least 200 L (44 gal), as one reference suggests.

Diet

Relies on light and on food. It keeps zooxanthellae and one aquarium reference calls it mostly photosynthetic, though no study has measured how much energy they supply. It also traps prey whole. Give moderate light and offer a small piece of fresh fish, clam or shrimp near the mouth about once a month, removing whatever it refuses.

Behavior & temperament

Any moving object that touches the disc can set it off. The rim folds up and draws closed like a drawstring within about three seconds, trapping prey with up to four litres of water. Trapped animals keep moving for 10 to 20 minutes before they stop, and whatever subdues them hits fish harder than invertebrates. Lab animals took everything from brine shrimp to large prawns and fish. The species is the only one in its genus.

Health

Eats fish. Brushing against the short tentacles is enough to start the disc closing on a fish or shrimp, and a fish sleeping on it overnight may be caught and eaten. Keepers have reported losses up to angelfish size, and newly added animals seem most at risk. One keeper also reported its sting badly damaging leather corals and Pocillopora, so keep it clear of corals. It is otherwise regarded as easy to keep.

Tips, DIY & hacks

Keep every fish you care about elsewhere, and think of it as a species-tank animal. Take care when adding new fish or shrimp, since new arrivals are the most at risk. Keep it clear of corals, because a keeper reported serious sting damage to neighbouring corals. Do not confuse it with the small Rhodactis called elephant ear, which is a different animal with very different size and appetite. Plan for its full width, because it is hard to rehome.