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Oulactis muscosa

Kana Newell 2015


O. Muscosa inhabits the intertidal rocky shores along the east and southern coast of Australia, as well as New Zealand and Tasmania. Their common name is the speckled anemone, suitable as they often bury themselves in particulate sand/shells. This is thought to be a mechanism for avoiding damaging UV light. Their distinct morphological characteristic is their Acrorhagi, which are used for defense against threats as well as maintaining territory. The acrorhagi are sticky, and contain specific nematocysts called holotrich’s, which discharge on contact. They reproduce sexually,where the planktonic larvae gets swept by strong currents and carried down the east coast of Australia, allowing a wide range of dispersal, although resulting in a genetically homogeneouspopulation.  Not much is known of the sea anemones phylogeny and systematic's, making the family or even species level near impossible to map. This is because they are poorly preserved in the fossil record, phenotypically plastic as well as structurally simple, making them difficult to classify. O.muscosa aren’t under any threat, as they aren’t being collected commercially. They are also in a high energy environment which allows constant movement of water, resulting in less potential for pollution, anoxic waters and other factors to threaten them. 

Physical Description

Cnidaria: The presence of cnidocytes, are diploblastic

                Anthozoa:polypoid cnidarians, with a pharynx that opens into the gastro vascular cavity

                                Hexacorallia: 6-fold symmetry

Actiniaria (sea anemones): Largepolyps, lack medusa stage, many symbiotic with zooxanthellae, popular in theaquarium trade.

Actiniidae: largest family ofsea anemones, mostly temperate shore species, no symbiosis with fish (althoughexceptions), one tentacle per space, most possess acrorhagi. 

Oulactis muscosa:

 O.muscosa is often seen covered in sand/shell fragments, giving it the common name thespeckled anemone. Anemones have high phenotypic plasticity, where varying colouror morphology may occur. O. muscosa is usually white on the lower column withadhesive verrucae moving up the column until it reaches the tentacles. Betweenthe tentacles are the acrorhagi (which is usually covered by sand/shellgrains). The tentacles have banded colouration (green- grey/white- purple), aretransparent and numerous.  They can reachup to 100mm in height and 50mm in diameter. 

Figure 1


O. muscosa is found in high energy, mid to low intertidal-rocky shores. They are often found in rock crevices, sand areas and go to a depth of 5m below the low tide mark. A symbiotic relationship with zooxanthellae occur, with this microscopic algae inhabiting the tentacles and upper column in the gastrodermal tissues. In anthopleura (family actiniidae, also on intertidal rocky shores, these algae photosynthesise and convert CO to reduced organic carbon, which is then integrated into the anemones tissue to be used for further synthesis. It’s been suggested that this symbiosis benefits the anemone in a nutritional way. 

As O.muscosa live near the water column/intertidal zone, it is assumed that it is often exposed to high UV rays due to constant sun exposure. Low levels of MMA (mycosporine-glycine amino acid) in the anemones body suggest otherwise, where low MMA levels indicate less ultraviolet absorbing molecules. Less MMA suggests that the anemone is in a low UV environment and do not need high levels of UV absorbing molecules to reduce cellular damage. Its mechanism for decreasing sun exposure is relocation to sub tidal areas/rock pools as well as the distinguishable behavior of burring in sand/sediment. The feeding ecology can be also reflected through MMA levels, as the mussel B. rodriguezi has significantly high levels of MMA in its body. Since O.muscosa are polyphagous opportunistic feeders, their diet varies, although the anemones that predominantly feed on the mussel has significantly increased MMA levels.  

Life History and Behaviour

Anthozoan’s are aggressive in nature, where attacking an anemone in close proximity is common. O.muscosa possess acrorhagi, a sac like structure containing nematocysts, which expel when in contact with a threat and may cause tissue death. 

There is no published information of O. muscosa behavior, although personal speculation/observation was made while handling 2 individuals of O. muscosa species. The individuals would cover itself in sand/shell grains in the aquarium, but would release the sand grounds when brought into the laboratory. This occurred on 4 occasions with an aquarium/lab switch over. Possible explanation could be due to light intensity where it was very continuous and intense in the aquarium and less intense in the lab. It could be due to the presence of other fauna in the aquarium (copepods,gastropods, anemones), where the O. muscosa were in isolation in the lab. Another explanation could be the constant disturbance in the lab, where poking and probing occurred, causing the anemone to release the sediment/sand and expose he acrorhagi in case aggressive behavior was needed. This behavioral response could have occurred for various reasons which should be further analysed and investigated.

The individuals were also placed in contact with genetically distinct anemone, in order to observe aggressive behavior. The O. muscosa contracted with initial contact of the invaders tentacle, exposing the acrorhagi as well as covering the tentacles and mouth (Fig.2, Fig. 3) . The invader constantly tried to move away from the O. muscosa individual, suggesting some deterrent or due received by the invader. The acrorhagi was also adhesive, sticking the other sea anemones tentacles to it (Fig. 4). 


O. Muscosa are dioecious, meaning they have two distinct male and female individual organisms/colonies at a 1:1 ratio. Most individuals found were sexually mature and collection went throughout the year. There have been no observation for asexual reproduction in this species, where only sexual reproduction was found to occur.  Their dispersal method is through planktonic larvae, which can be carried to a range of up to 735 km along the coast. The planktonic larval distribution is heavily affected by the currents of the southward flow on the east coast as well as westerly flow along Australia's south coast. This allows mixing of larvae through populations, which ultimately results in a homogenizing effect on the genetic structure (less genetic diversity) of these populations along Australia’s east coast. Although genetic subdivision was found along the south coast. Homogeneity has been proven as samples collected along the O.muscosa's distribution range show over all low genetic differentiation. 


Figure 2
Figure 3
Figure 4

Anatomy and Physiology

A longitudinal cross section of an individual O. muscosa using histolological staining was taken. Below are the definitions of the anatomical sections distinguished in this cross section, as seen in Fig. 5. 

Tentacle: Surround the oral disk and contain cnidocytes, they can be used defensively or for feeding.

Endocoelic chambers: The space between two mesentries belonging to the same pair.

Actinipharynx: Essentially the throat/pharynx. It’s the tube that leads from the mouth into the coelenteron (gastric cavity), where digestion, nutrient absorption and gas exchange occurs.

Verrucae: Eversions of the column that are mostly known for its adhesive properties as it contains no nematocyts.


The mesentries are arranged in pairs and are located systematically along the anemone. Despite the anemones radial appearance, they are actually biradial, one part due to the mirroring mesentrial pairs. They extend from the body wall into the coelenteron,and occasionally up to the actinopharynx, to create a endocoelic chamber which the primary mesentries are responsible for enclosing.  The tertiary mesentries are incomplete and do not reach the actinopharynx.

Mesenterial filaments: Aid with digestion and internal water movement, located at the terminating end of the complete mesenteries. In some species they form acontia which is used for defence. 


The anemones muscles are comprised of the longitudinal muscles fields (1), the radial muscle fields (2),the circular muscle fields (3) and the oblique muscle fields (4) (Fig. 6).  The longitudinal muscles constitute the retractors (Fig. 7) on the mesenteries as well as contribute to tentacle control (through endoderm), The radial muscle fields constitute basilar and transverse muscles on the mesenteries, and control of the oral disc (Fig. 8). The circular muscles control the marginal sphincter and parts of the tentacles and the oblique muscle fields are the parietobasilar muscles that line a side of the mesenteries associated. 

Sphincter muscle: Circular muscle located near the margin (upper column near tentacles), Larger in inter-tidal anemones where incoming wave energy and pressure is higher. 

Acrorhagi (Fig. 9)

Are specific to Actiniaria and are outgrowths of the body wall located between the tentacles as well as further down the column. O. muscosa showed branching of the acrorhagi,which were transparent and pink/orange in color. When acrorhagi respond with aggressive behaviour, they stick to the victim and then  discharge holotrichous nematocysts, which area defining characteristic of acrorhagi. Tissue death may occur in the victim several days later, occasionally resulting in death. 

Figure 5
Figure 6
Figure 7
Figure 8
Figure 9

Evolution and Systematics

Sea anemones are very phenotypically plastic and structurally simple, making them very hard to classify. They lack skeletal parts which results in lack of anemones in the fossil record, with preserved species being poor. We are currently taxonomically arranging sea anemones based on morphological characteristics (tentacle arrangement, shapes of muscles, nematocyst specification), although these can be unreliable as they vary with morphological changes in developmental/nutritional state, asexual reproductive stage  and environmental restrictions. Phylogeny within Actinaria (sea anemone) order is met with high disagreement, and no uniform conclusion has been drawn yet. 

Biogeographic Distribution

Oulactis muscosa is present along the Australian coast from southern Queensland through New south whales, Victoria and south Australia as well as Tasmania and new Zealand. 

Figure 10

Conservation and Threats

O.muscosa is not listen on any conservation lists including DSE advisory list, EPBC act 1999 and IUCN red list. There is no interest for O.muscosa in the aquarium trade and are therefore not collected, resulting in no threat. 


Arbeloa, E.M., Carignan, M.O., Acuña, F.H., Churio, M.S. & Carreto, J.I. 2010,"Mycosporine-like amino acid content in the sea anemones Aulactinia marplatensis, Oulactis muscosa and Anthothoe chilensis", Comparative Biochemistry and Physiology, Part B, vol. 156, no. 3, pp. 216-221.

Daly, M., Chaudhuri, A., Gusmão, L. &Rodríguez, E. 2008, "Phylogenetic relationships among sea anemones(Cnidaria: Anthozoa: Actiniaria)", Molecular phylogenetics and evolution, vol.48, no. 1, pp. 292-301.

Department of the Environment, Biodiversity: Australian Biological Resources Study, Government of Australia.

France, S.C. 2004, Anthozoa (Anemones and Corals).

Hunt, A. & Ayre, D.J. 1989, "Population structure in the sexually reproducing sea anemone Oulactis muscosa",Marine Biology, vol. 102, no. 4, pp. 537-544.

Leonard, M. 1971, “Experiments on Green Algae Coexist withZooxanthellae in Sea Anemones”, Pacific Science, Vol. 25, pp. 13-21.

McCommas, S.A. 1991, "Relationships within the family Actiniidae (Cnidaria, Actiniaria) based on molecular characters",Hydrobiologia, vol. 216-217, no. 1, pp. 509-512.

Patronelli, L., Zamponi, M. & Olivera, E.G.2005, "Influence of the intertidal environment on muscle activity indifferent species of sea anemones (Actiniaria)", Animal Biology, vol. 55,no. 2, pp. 101-109.

Shick, J.M. 1991, A functional biology of sea anemones, Chapman & Hall, London ; Melbourne.

Tullock, J. 1998, ‘Clownfish Host anemones' in Clownfish and Sea Anemones, Barron’s Educational series, pp. 42-48.

Williams, R.B. 1991, "Acrorhagi, catch tentacles and sweeper tentacles: a synopsis of 'aggression' of actiniarian and scleractinian Cnidaria", Hydrobiologia, vol. 216-217, no. 1, pp. 539-545.