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Marine Invertebrate of the Month
Issue: October 2009

Amplexidiscus fenestrafer

DUNN & HAMNER 1980

Iom T 1009

Bob Goemans

Common Names: Elephant ear coral, giant cup mushroom

Phylum: Cnidaria (soft corals)

Class: Anthozoa

Order: Corallimorpharia

Family: Discosomatidae

Range: Tropical Indo-Pacific Ocean

Natural Environment: Thought to be the only species in its genus, this coral is found in shallow waters in lagoons and tidepools, often in turbid and still waters. It is generally a tan color, but depending upon where it was collected, the elephant ear coral may be ivory, dar

Captive Care:

These mostly photosynthetic corals, which can attain a diameter of 12 to 14 inches, are among the easiest of all large-polyped soft corals to maintain since they do better in somewhat nutrient-rich surroundings with medium light intensity and gentle water movement. They are not true anemones, nor are they true corals. However, they are closely related to both organisms—being somewhere in between—and more study is needed to define precisely what they are.

This is a large polyp that can actually change its shape fairly quickly (sometimes within a few seconds) from an open and flat disc-like form to a closed, onion-shaped polyp and trap an animal inside, which it will then eat. In fact, any fish or shrimp crossing over its broad surface that touches its short tentacles will trigger a closing action. Nevertheless, most animals seem to realize the danger and do not risk lingering on its surface. Yet during evening hours, if a fish attempts to sleep on the coral’s open surface area, it may become trapped inside, where it will become breakfast.

Directly hand feeding this species is not necessary because it is largely a photosynthetic animal, quite similar to the common mushrooms and capable of absorbing dissolved nutrients directly from the water. Nevertheless, occasionally (i.e., once a month) placing a small piece of fresh fish, clam, or shrimp flesh near the central mouth area will usually trigger a closing action and the consumption of the food. Feeding small elephant ear corals will result in fairly quick increases in growth, but adult size remains as noted above.

If the food is not consumed, remove it and try a few days later. I’ve had this species a few times and almost always found it to like an occasional snack. If the elephant ear continues to fail to take a tasty snack, it may be due to aquarium conditions such as light intensity and water quality/movement, so it may need to be moved to a new location in the tank. The ideal areas are on the bottom substrate, where currents are gentle and there is reduced light intensity. And as to location, I’ve found the species to be much like large sea anemones, with each species finding a preferred location in my aquariums; unfortunately this species is incapable of moving itself, so the aquarist must decide its best placement.

Water Requirements: Calcium 380 to 430 ppm, alkalinity 2.5 meq/l, pH 8.1 to 8.2, specific gravity 1.025, nitrate <30 ppm, phosphate <0.015 ppm, and a temperature range of 72° to 83°F. Iodine additives, used to their manufacturers’ recommendations, also seem to have a positiv

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