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Marine Invertebrate of the Month
Issue: July 2009

Rhodactis mussoides

(SAVILLE-KENT 1893)

IOM 0709

Bob Goemans

Common Names: Elephant-ear mushroom coral, giant mushroom, mushroom polyps, disc anemones, hairy mushroom

Phylum: Cnidaria

Class: Anthozoa

Order: Corallimorpharia

Family: Discosomatidae

Range: Tropical Indo-Pacific Ocean

Natural Environment: These common photosynthetic soft corals are usually found on reef slopes, bays, lagoons, boat channels, and in shallows and backwaters where turbid and more nutrient-rich waters collect. Their colors are various shades of green and/or brown depending upon

Captive Care: Rhodactis are extremely easy to maintain, as they require only low to moderate light, some water current, and a somewhat nutrient-rich environment for keeping them healthy and happy. This particular species is usually olive green, with a white or pink central oral area. Its large, usually somewhat folded polyps have a leathery texture, and the species can reach 8 to 10 inches in diameter or even slightly larger depending upon its surroundings. There are no outer edge tentacles, and its edges are sometimes ruffled. They are usually called hairy mushrooms because of their many small, fuzzy tentacles, but polyp surfaces on this species are more pimple-like. Their polyps can also fold upward to a certain extent and appear somewhat onion-shaped, but they do not use them to trap animals inside and eat them. If edible foods settle on their upper surface (e.g., detritus), they may form an onion shape that helps their cilia move the edible items toward their centrally located mouth, but this occurs very slowly. The mushroom’s main nutrition is provided by its zooxanthellae and the absorption of dissolved nutrients in the water. Some polyps can have multiple mouths and divide by longitudinal fission. This often begins at the central orifice/mouth and extends across the whole disc. Since this species is somewhat aggressive (except to those in the same genus), R. mussoides should not be placed within touching distance of other corals in the aquarium. They are very hardy, disease resistant, and under the right circumstances, fairly fast growing. Though the word “anemone” may be used in their common name, they are not true anemones (order Actiniaria), nor are they true corals (order Scleractinia). They are all in the subclass Hexacorallia, but mushrooms are in the order Corallimorpharia. Reproduction-wise, for those who can’t wait for nature to take its course, the entire head of the stalk can be cut off and then cut into several pie-shaped pieces. Those pieces can then be placed in a shallow tray of very coarse sand with gently flowing water across its surface area. In a few days, those individual pieces will attach themselves to the substrate particles and form new polyps in due time. The cut stalk will regain its original shape, and in the coming months it will appear no different than it did before the cutting.

Water Requirements: Calcium 380 to 430 ppm, alkalinity 2.5 meq/l, pH 8.1 to 8.2, specific gravity 1.025, and a temperature range of 72° to 83°F (22° to 28°C). Iodine additives, used under manufacturers’ recommendations, also seem to have a positive effect.

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