Sea anemones have long been of interest to marine aquariumkeepers, especially those species that host anemonefishes (especially anemones in the Heteractis and Stichodactyla genera). However, there are many unusual anemone species that occasionally make their way into the pet invertebrate trade that are often overlooked by aquarists. Many of them do not host piscine symbionts, but they are equally as attractive and interesting. But beware — the potent sting of some of these anthozoans is only rivaled by their beauty!
All of the sea anemones considered in this article are known to provide a home to various crustaceans. But a more vital symbiotic relationship exists between these sea anemones and microalgae (known as zooxanthellae, Symbiodinium species). The anemone provides a place for these algae to grow, while the nutrients produced by these algae during photosynthesis are utilized by their hosts. (To see more about how to provide good growing conditions for these microalgae, see the “Anemones and Light” sidebar.)
While these anemones rely heavily on algae symbionts to provide nutrients, they do best if they are also fed. The amount of food you give them will depend on how fast you want them to grow (more food means faster growth), how fast you want them to reproduce (more food equals more asexual reproduction) and how intense the aquarium light is (the lower the light levels, the more nutrients they will acquire by ingesting food). Most sea anemones will be fine with a piece of meaty food once or twice a week. This could be a piece of table shrimp, whole mysid shrimp, pieces of scallop, mussel tissue and marine fish flesh. The food item should be a quarter of an inch to 2 inches in length, depending on the size of the anemone. If food items are too large, they will reject them. If the food item is frozen, let it thaw completely before placing it on the anemone’s disc. Some species (e.g., Phyllodiscus semoni) should be fed after dark.
Powerheads and water pumps placed in the aquarium can be an anemone’s worst enemy. Pump intakes must be blocked to prevent the malleable tentacles of the anemone from getting caught in the pump impeller. The best way to do this is to place a sponge filter on the intake of the powerhead (a simple strainer is not adequate). Prop pumps are also potentially deadly to sea anemones, as the anemones may be attracted to the water movement and get wrapped up in the propeller. If your anemone gets caught in a water pump, unplug the pump and see if the anemone will extract itself on its own. If this does not happen, “surgery” will be required. Unfortunately, most anemones die after such extractions. Heaters can also burn anemones that contact them. It is best to place heaters in the sump or construct a PVC sleeve with slots cut into it to make contact between the anemone and the heat source less likely to occur.
Moving an anemone from one tank to another can also be a challenge. If it is attached to a small enough piece of rock, move both the anemone and the rock in order to avoid tearing the anemone’s base. If you have to remove the anemone from the rock, lift both from the water and place an ice cube at the edge of the anemone’s base. This often causes the anthozoan to gradually release its grip. If this does not work, take a credit card or other instrument with a dull plastic edge and gently work the plastic edge under the anemone’s base. Remember that if you remove an anemone by tearing its tissue, it can result in its death.
Sea anemones present some special compatibility challenges. Most anemones have potent stinging cells (cnidae) that will damage the tissue of many of their “stay-put” relatives if they should come into contact. If the anemone is a sand-dweller, it will be easier to keep it away from corals that can be placed higher up on the rockwork. Anemones that move on and attach to hard substrate are more likely to cause problems. Some of the species described in the following “Anemone Species” section are particularly toxic and will not only destroy the tissue of stony and soft corals they contact but can cause harm to you as well.
Hell’s fire anemone (Actinodendron spp.). This genus and two other genera belong to the poorly known family Actinodendronidae. There are at least six species in this genus, with several occasionally making their way into the aquarium trade (Megalactis hemprichii, another member of the family, is also seen in fish stores on rare occasions). These sea anemones have highly branched tentacles, which have caused some to misidentify them as soft corals. The resemblance may be a case of aggressive mimicry. By resembling benign soft corals, they may attract small fish that wish to take refuge within the branches. These imposters consume fish that mistake them for their soft coral look-alikes.
The color of these animals is usually not show-stopping. Some do sport white lines radiating out from the central mouth, purple on the disc or an overall greenish or grayish-blue hue, but most are brown. All members of the family are found in the Indo-Pacific and prefer protected coastal habitats. These anemones serve as hosts to Leander (e.g., L. tenuicornis) and Periclimenes shrimp (e.g., P. inornatus), as well as the beautiful harlequin crab (Lissocarcinus laevis).
It might not be a surprise (considering the common name), but these anemones have a nasty sting. Always wear gloves when working in a tank that contains an Actinodendron anemone. Be aware that they are also dangerous to fish tankmates, though most fish species know to avoid them. Species that bounce along the bottom (e.g., scorpionfishes, frogfishes, seahorses, pipefishes and dragonets) are most likely to accidentally contact the cnidae-laden tentacles.
The Actinodendron species are hardy aquarium anemones, but they do have one special requirement: a 6-inch or deeper sandbed. These anemones will plunge their bases and columns down into the soft substrate and leave only the tentacles exposed. When threatened, they may even retract their tentacles under the sand surface. One Actinodendron habit that can be a bit disconcerting is that they occasionally produce copious amounts of mucus. When they do this, they may float about the tank. This is when they are the most dangerous to their sessile invertebrate neighbors, as the Actinodendron will sting them if they collide.
Berry anemone (family Thalassianthidae). Anemones in the Thalassianthidae family are interesting animals, and their systematics and biology are poorly known. The most familiar member of the family is the pizza anemone (Cryptodendrum adhaesivum). This species is flat with short tentacles; the shorter tentacles along the margin are similar in appearance to the crust on the edge of a pizza. It is the only member of the family that sometimes hosts an anemonefish (Clark’s anemonefish, Amphiprion clarkii).
Another more attractive member of the group is Heterodactyla hemprichii. This species occurs from Indonesia to the Red Sea and can grow to about 12 inches across the disc. It is a beautiful cnidarian that superficially resembles the well-known carpet anemones (Stichodactyla spp.). It has a round, flattened disc like its carpet cousin, but it differs in having finely branched tentacles and berrylike structures (known as nematospheres) along the disc edges. The “berries” are often very colorful. They can be purple with a bright green center or blue with a central yellow spot. The disc of this species can be white, green, brown (most common in the trade), red or purple, while the column is usually whitish (but it can be purple) with purple verrucae. There are two other species listed in the genus Heterodactyla, but they are poorly known, and one or both may not be valid species.
There are also Thalassianthus species (three valid species), particularly T. aster, that make it into the aquarium trade. Thalassianthus aster is usually tan with some light green highlights. It is sometimes imported on live rock or on mushroom or zoanthid rocks. Next to C. adhaesivum, this is the most common thalassianthid in the aquarium trade.
Members of this family tend to occur on consolidated rubble and other hard substrates. In the aquarium, they will attach to live rock and do not require a sandbed to thrive. At first they may migrate about the tank until they find the perfect perch. Thalassianthus aster does not pack a potent punch, but Cryptodendrum and Heterodactyla are strong stingers that will damage any coral or anemones that they contact. Wear gloves when handling Heterodactyla, as they can also sting you. Some of the berry anemones, such as Thalassianthus aster, are prolific splitters and can become pestilent in the aquarium because they reproduce so rapidly. Feed these anemones frozen mysid shrimp and smaller food particles that will stick to their relatively short tentacles. The thalassianthids host Thor and a number of Periclimenes shrimp, some of which (e.g., P. brevicarpalis) may occasionally feed on their tentacles. If the anemone is healthy, occasional tentacle browsing by this shrimp causes little harm.
Antler anemones (Lebrunia spp.). These anemones are members of the Aliciidae family and are found on Western Atlantic coral reefs and adjacent seagrass beds. They are attractive anemones that usually affix themselves to hard substrate, often secreting their bases and columns deep into reef crevices so that only their branching pseudotentacles are visible during the day. The pseudotentacles harbor most of the zooxanthellae — 20 to 30 times more than the “true” tentacles. The threadlike true tentacles are retracted during the day and employed at night to capture zooplankton. The tentacles are usually clear but may have colorful tips. There are also round vesicles (which can be blue in at least one species) among the branching pseudotentacles that contain the stinging cells. The most commonly encountered species in the aquarium trade is Lebrunia danae, which is commonly called the antler anemone.
The antler anemones are durable aquarium animals that do well in moderate- to high-light conditions. Under more intense illumination, you may find that your Lebrunia stays in more shaded microhabitats in the aquarium (under ledges where they get indirect light).
This is a powerful stinger that can cause severe pain — or on very rare occasions paralysis or even death. The venom in this animal is actually a neurotoxin, so make sure to wear gloves when working in the aquarium. Antler anemones can sting and do extensive damage to their coral neighbors as well. Therefore, be cautious about dropping an antler anemone into your reef tank. Instead, you may want to house one in a nano reef where it can be the featured sessile invertebrate. You could also add one or more of the crustaceans that it regularly hosts, including several Periclimenes species (including P. pedersoni), the sexy shrimp (Thor amboinensis), arrow crabs (Stenorhynchus seticornis) and the commensal spider crabs (Mithraculus cinctimanus). This anemone is preyed on by the aeolid nudibranch Spurilla neapolitana, which take the stinging cells of this sea anemone and store them in the appendages on their backs (known as cera).
Delbeek, J. C. personal communication.
Delbeek, J. C. and J. Sprung. 1997. The Reef Aquarium, Volume 2. Ricordea Publishing, Coconut Grove, Florida. Pp. 546.
Fosså, S. and A. Nilsen. 1998. The Modern Coral Reef Aquarium, Volume 2. Birgit Schmettkamp Velag, Bornheim, Germany. Pp. 479.
Lougher, T. 2011. “Top of the Rocks: Anemones.” Marine Habitat 6: Nov-Dec: 31-35.
Mok, M. 2010. “Mini-Carpets: The Perfect Small Sea Anemones?” Coral Magazine
Night fire anemone (Phyllodiscus semoni). This anemone (also a member of the Aliciidae family) is occasionally encountered in the aquarium trade. It is a particularly funky species that exhibits a variety of different morphotypes (forms). In the past, some of these forms were once thought to be distinct species. It has been hypothesized that P. semoni mimics other life forms in its environment (e.g., stony corals, soft corals, macroalgae patches or rocks covered with filamentous algae) to throw off anemone predators (e.g., specialized butterflyfishes, sea turtles) or to attract smaller prey items, which it then consumes. In some cases, the likeness of this anemone to apparent models is uncanny. For example, it can look just like Seriatopora, Pocillopora, Porites and Anacropora stony corals, or Briareum and Sinularia soft corals. The color of this species is also variable, with individuals being brown, green or even bright orange.
Like Lebrunia species, this animal possesses vesicles on the disc and column known as pseudotentacles. These structures are responsible for the differing morphotypes of P. semoni and harbor sting cells and zooxanthellae. During the day, the “true” tentacles are retracted into the coelenteron (the simple saclike body cavity of a coelenterate), while at night they are unfurled to capture minute prey. The night fire anemone can be found on its own or in aggregations. Aggregations are apparently the result of the splitting of a mother colony to create a group of clones. It is often found among dead coral branches or consolidated coral rubble.
This hardy animal is toxic, and if you decide to keep one, treat it with the utmost respect. This includes putting it in a place in your home where the aquarium will not be accessible to children. In most cases, contact with the tentacles will result in skin irritation, blisters and necrosis, and resulting lesions may take a while to heal. In rare cases (at least one reported case), the toxin has been known to cause renal failure and death. When working in the tank, it is imperative you wear gloves. This anemone is a known host to anemone shrimp (e.g., Periclimenes brevicarpalis, P. venustus) and is sometimes parasitized by wentletrap snails (Epitonium spp.).
Beaded sand anemones (Phymanthus spp.). This genus is comprised of 10 species that belong to the Phymanthidae family. They are also referred to as flower or beaded anemones. At first glance, some of the members of this genus resemble the aurora anemone (Heteractis aurora), especially the species that have swollen nodes or cross-bars along the tentacle length. The members of this genus can be found in shallow tropical seas around the world. The number of species has yet to be determined, but it appears that there are at least 10. Some are very colorful — the column can be orange, while the tentacles can be green, red, lavender or maroon. That said, they are more often a subdued gray or brown.
Phymanthus species are usually found on soft substrates but often will attach to rocks resting on or partially buried in the sand. In the aquarium, it is important to provide a sandbed in which these animals can hide their bases. Fortunately, their nematocysts are not as potent as others, and they can be kept in reef aquariums without causing problems with fish or invert neighbors. While wild anemonefishes do not occupy the sand anemones, some less selective species (e.g., Amphiprion clarkii) may refuge among their tentacles in captivity. They often host Periclimenes (e.g., P. brevicarpalis) and sexy shrimp (Thor spp.), as well as anemone crabs (Neopetrolisthes spp.).
These anemones are dioecious (there are separate males and females), and they brood their young (meaning that the eggs are fertilized and develop in the female before they are expelled as larval anemones). These anemones do not reproduce asexually.
Maxi-mini carpet anemone (Stichodactyla tapetum). This beautiful little Indo-Pacific anemone came bursting onto the North American scene about four years ago, and it has taken the industry by storm. The colors that it displays are mind-boggling and can include red, maroon, orange, blue and bright green, with some individuals displaying a combination of these bold colors.
There are at least two species or possibly morphotypes; the disc of one grows to about 2 inches in diameter (often just called mini-carpets) and a type that grows to about 5 or 6 inches in diameter (maxi-mini carpets). Some reports also discuss an even larger form (up to 12 inches across). While most specimens are imported from Vietnam, some of the available S. tapetum are the result of aquaculture efforts. These anemones reproduce by asexual fission, but if you are too impatient to wait for this natural propagation to occur, cut your maxi-mini in half with a very sharp razor blade or scalpel. Soak both halves in a saltwater/iodine bath, and you have two smaller anemones that will be good as new in a month or so.
The other thing that makes S. tapetum an aquarium winner is that it is hardy. Just give it in an aquarium with moderate to high light and decent water movement, and it will thrive. Unlike some others in the Stichodactyla genus, it prefers to attach to rocky substrate, so it may travel over your reef structure until it finds a preferable perch. However, it does not have as potent a sting as some of its relatives, and they usually only cause minor turf war issues with other cnidarians. Its less potent sting and small size make it less of a threat to fish tankmates, though it is a threat to Mandarin dragonets and small benthic fish. It will host shrimp, including Periclimenes species and Thor amboinensis, as well as anemone crabs.
That ends our survey of some of the more anomalous anemones. I hope you will give some of these interesting animals a try in either a large reef community tank or will feature them in a smaller nano reef setting. For the sake of your corals and yourself, make sure you are aware of the stinging capabilities of any sea anemone before placing it in your aquarium. Happy cnidariankeeping! AFI
Scott W. Michael has kept marine fish for more than 25 years. He is the author of Reef Sharks and Rays of the World; Reef Fishes: A Guide to their Identification, Behavior and Captive Care and more.