Aiptasia Biology
Originally posted in 2006
Updated in 2025
Phylum: Cnidaria
Class: Anthozoa, Zoantharia (Hexacorallia)
Order: Actiniaria
Family: Aiptasiidae
Physical Description: Called the “Pale Anemone” and “Glass Anemone”, it is a small anemone, having an oral disk diameter of no more than about 2 cm and a height of 5 cm. It is dark brown to pale gray in color, has a slender column, and a mixture of a few long and many short tentacles. The mouth opens at one end of the coelenteron and marks the oral end. The mouth is at the tip of a process, the manubrium that elevates it above the oral surface.
The opposite pole is the aboral end. The imaginary line connecting the oral and aboral poles is the axis of symmetry around which the radial symmetry of the body is organized. The mouth is surrounded by one or more rings of up to 100 tentacles anchored toward the outer part of the oral surface.
Like all cnidarians, all aiptasia species exemplify the tissue level of organization and are composed of two cell layers: an epidermis and a gastrodermis. The two cell layers are cemented together by an acellular matrix known as mesoglea. Like other anthozoans (zoanthids, anemones, corals), the gastrovascular cavity of aiptasia sp. is partially subdivided by radially arranged septa containing string-like acontia and gonads along their inner edge.
Symbiotic single celled dinoflagellate algae, zooxanthellae, are found within the gastrodermal cells. Both the acontia and epidermis harbor cnidocyte stinging cells capable of capturing and subduing small prey (zooplankton), stinging fish, killing or causing tissue regression in sessile invertebrates or corals and pack a lethal sting to larval fish and young seahorses. Cnidocytes are generally harmless to humans although in large numbers they may cause noticeable irritation to sensitive skin. Unlike some cnidarians, aiptasia are extremely successful in generating or regenerating an entire animal from a single cell. It is this tissue level of organization that makes the aiptasia anemone so difficult to eradicate from your reef.
Sexual Reproduction: A look deep inside the Aiptasia at the coiled mass of Planula Larvae. These are the oval bodies inside the membrane incorporated with scattered golden Zooxanthellae cells. When released into the currents, these Aiptasia Larvae colonize thousands of areas.
(Magnified x400+)
Reproduction is both sexual and asexual. Asexual reproduction is referred to as basal (or pedal) laceration. During this laceration of the foot, small bits of tissue bud from the periphery of the anemone’s radially arranged basal disk. Within the radial arrangement, the divisions of the basal area isolate these little “seeds” from the larger part of the anemone. Migration and division from the foot may take a few days to a week when the anemone is left undisturbed.
When migration from the main anemone is completed, the little “seeds” are already capable of producing as many as 30 to 40 additional identical little clones. Within a week or two after completely separating from the foot the bud develops a mouth and small tentacles and begins to feed on its own.
Basal laceration is a very easy and efficient method for the anemone to reproduce and leave behind many identical little clones that go unnoticed for some time. Some of these clones will release and be distributed in the water column to colonize other locations. Aiptasia sp. increase asexual reproductive basal lacerates during times of extreme stress such as low oxygen, decreased circulation during power failures, low lighting situations (rock slides, new additions to the tank, coral growth resulting in shading), attack by predators and when the reef keeper attempts physical or chemical methods. If the reef keeper is successful in destroying the main body of the adult Aiptasia with injections, fish or shrimp, then all of the Basal Cells and Planula Larva are released at once to start growing and colonizing parts of the reef independently.
In this case the umbrella of the main adult Aiptasia is removed so these basal cells now have free access to light, currents carrying nutrition and water rich in oxygen. Basal lacerations may remain and disperse through the system for up to a year after what appears to be a successful attack on one anemone by a larger predator (shrimp, fish, crabs) or the reef keeper. Planula colonize numerous areas and remain hidden until the timing is optimal for them to grow.
Once this growth begins, they can quickly become a plague of Aiptasia growth.
In sexual reproduction, oocyte sizes and gonad weights as well as asexual basal lacerations increase with more light and more feedings or nutrients. However the reef keeper should not assume that nutrient poor water and reduced fish feedings will slow the process any because aiptasia contain zooxanthellae.
Zooxanthellae, the single celled dinoflagellate algae of the genus Symbiodinium are surrounded by a host derived membrane forming a vesicle known as the symbiosome. The symbiosis is mutualistic. The algae have access to nutrients (IE: N and P) which would otherwise be in very short supply. These compounds are produced as metabolic waste products of the host (IE: NH_{4}+). We should also take time to note here that in the absence of adequate nitrogen food sources, dinoflagellate algae colonies can develop a cell center that can fix dissolved atmospheric nitrogen and convert this as a nutrient source.
The host, in turn, receives photosynthetic products (mainly as glycerol) from the algae and in this has a reliable supply of carbohydrates to furnish it with energy. The anemone gives the dinoflagellate a place to live which is high in minerals and in return the anemone is fed glycerol by the dinoflagellates. Glycerol, an important product of photosynthesis, chemical formula C_{3}H_{8}O_{3}, is commonly referred to as a sugar or sugar alcohol. It can have a xanthochromatic (yellow to yellow gold) tint.
Glycerol is the backbone of triglycerides and phospholipids and is a good source of carbon and energy. These are important building blocks in animal biology. The dinoflagellate starts the synthesis for a living source of protein and carbohydrates! Using HPLC-EC (high pressure liquid chromatography) dopamine and serotonin (5-hydroxytryptamine, 5-HT) can be found in both tentacles and the Aiptasia’s body. Dopamine affects the central nervous system, serotonin brain activity and balance.
Why are these amino acids present at all in an animal completely lacking a brain and with only a rudimentary nervous system? At this time it is unknown how these proteins react with chemicals used on the host anemone or its effect on corals in a closed system. It is possible these compound the problems of the chemicals and is an additional contributor to the mystery death seen in some species of corals within days to weeks following the use of currently marketed and widely accepted chemical methods used against the host aiptasia.
It is certain that nutrients are released and not exported from the system when aiptasia are attacked chemically or physically unless this is done in a separate container isolated from the main system.
In tanks with Aiptasia, reproduction by sexual means as well as asexual lacerates results in settling of gametocytes and spreading of cells forming an intricate biofilm on the rocks.
The dispersal of new Aiptasia cells combined with the tissue level of organization means that a good target natural predator is eventually necessary for complete aiptasia harvest. Adult Berghia nudibranchs are the only animal that can get down into the holes, under shells and between rocks to remove the Aiptasia at the root of the problem. Berghia are also the only Aiptasia predator that do not cause the Aiptasia to spawn as they touch first just like a clownfish.
The Aiptasia can sense the nudibranch’s presence but the nudibranch withdraws on the first couple of contacts in similar fashion as a clownfish entering a new anemone host. It is also helpful in the culture of Aiptasia anemones to know about their reproductive capacity. It may take some time for the small Aiptasia cells to become visible Aiptasia, but given the time, they will. Successful Aiptasia culture is beneficial in the laboratory setting for study and rearing of Berghia nudibranchs.
Many projects can be done with these two animals and if one is to provide extermination of the Aiptasia in a coral reef, understanding the creature we’re after will help us be successful. In the case we are involved in medical research, this could still be another source for a cure.
