Some of the large-polyped stony corals make incredible display animals in the reef aquarium. Probably one of the most stunning of these is the hammer coral or anchor coral (Euphyllia ancora). The hammer coral has a large polyp with long tentacles that often exhibits bright colors. The tentacles also move about, which adds some motion to the reef aquarium.
Difficulty: Euphyllia ancora and other members of the genus Euphyllia tend to be fairly durable corals. It is important to keep alkalinity and calcium levels at acceptable levels, and to keep phosphate levels down, as it can hamper calcification. The hammer coral also relies on zooxanthellae (symbiotic algae) and captures food to meet its nutritional needs (you should also feed this coral meaty foods several times a week).
Physical description: The hammer coral has unique tentacles that have anchor, hammerhead or sausage-shaped tentacle tips. The color of the polyp can be brown, bright green, yellowish-green, gray and a pinkish coloration. The hammer coral can find large colonies and cover huge areas of reef. It is very similar to Euphyllia paraancora. They are easily differentiated by looking at the skeleton. Euphyllia ancora has a corallite that is called a flabello-meandroid (that is, it has a valley but does not share a common wall with the corallite next to it), with the tentacles arranged along the length of the skeleton. Euphyllia paraancora, in contrast, has a branching skeleton, and the polyps are arranged in a circular pattern in the corallite.
Range: The hammer coral is found from the Maldives east to Papua New Guinea and the Great Barrier Reef. The hammer coral is usually found on protected fringing reefs, sometimes in vast fields that cover thousands of square yards.
Compatibility: The hammer coral is a very strong stinger and can damage other stony corals placed near to it. Make sure you keep a buffer zone of a least 5 or 6 inches around your Euphyllia ancora. It turns out that it is not a danger to most other members of the genus Euphyllia, excluding the torch coral (Euphyllia glabrescens). A group of Euphyllia species packed next to one another can make for an very interesting display. The stinging cells have such a potent toxin that some aquarists will react stringing to the stings of this species (it usually consists of welting). Be sure that you do not touch your eyes after handling an Euphyllia ancora. The fleshy polyp of Euphyllia ancora will be fed upon by many butterflyfish, triggers and puffers. Other fish that may nip at them occasionally, especially if they are not well-fed, include angelfish (e.g., Centropyge spp.), surgeonfish and rabbitfish. The long tentacles of this coral may serve as a surrogate host to anemonefish. If the coral is healthy, the bathing of an anemonefish usually does not bother the Euphyllia ancora.
Aquarium conditions: The hammer coral can be housed in a smaller reef aquarium, but be prepared — it grows large and can grow quickly. The hammer coral will do well under low to moderate light levels (it will also thrive under more intense lights). Power compact and T-5 fluorescents will do (although you can also employ metal halides). You do not want to have your hammer coral pummeled by strong water currents, and it does best when subjected to low or moderate levels of water movement. Water parameters for the hammer coral are: calcium 400 to 450 ppm, alkalinity 3.2 to 4.8 meq/L, no phosphates and a water temperature of 76 to 84 degrees Fahrenheit.
Care considerations: Avoid individual hammer corals where the tissue is separating from the skeleton. Also avoid individual hammer corals that have brown goo on the polyp (this is known as “brown jelly” and is thought to result from an infestation of protozoa in the genus Helicostoma). If a hammer coral comes down with this infection in your aquarium, remove it immediately and giving the coral a 5-minute freshwater dip (the dip water needs to be the same temperature and alkalinity as the display aquarium water). Then put the hammer coral in front of a moderate current source. The skeleton of Euphyllia ancora is susceptible to boring green algae, which can eventually cause the demise of the polyp.
Breeding: The hammer coral is thought to have separate sexes (it is not a hermaphrodite). The hammer coral may brood larvae as well as release gametes into the water column. The hammer coral also reproduces asexually by producing daughter colonies, which show up at the base of the parent coral. It is possible to cut a parent colony into pieces, but this always leads to some tissue damage and may result in bacterial infections.