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You are here:   animal list > Actinia tenebrosa



Actinia tenebrosa (Farquhar1898)

Waratah anemone

Yiwen Yvonne Loh (2011)


Fact Sheet


Brief Summary

Physical Description


Identification Resources


Biogeographical Distribution

Local Distribution and Habitats

Life History & Behaviour

Life History & Behaviour

Evolution & Systematics


Morphology and Physiology

External Morphology

Internal Anatomy

Cell Biology



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Life history

Large, solitary polyps that lack the medusa stage, therefore the poly assumes both sexual and asexual reproduction


Feeding: Opportunistic feeders that rely on water currents to carry prey towards their tentacles. The large thick tentacles are armed with nematocytes that discharge toxins capable of paralysing the prey upon contact. Once immobile, the prey is transferred to the mouth by muscular action of the tentacles. The mesenterial filaments contain both digestive enzymes and nematocysts, these filaments can be discharged through the mouth or the cinclides at the approach of their prey.       

Reproduction: Species is viviparous with a mixture of sexual and asexual reproductive modes. It was suggested that sexual reproduction was used for the production of widely dispersed colonists (Ayers et. al., 1991) through broadcast spawning and external fertilisation and asexual reproduction such as brooding to expand within a given habitat. Brooding in which there is internal fertilisation and the embryo develops internally within the coelenteron of the adult anemone. Both male and female adults, without gonads, can brood juveniles within their coelenteron. Fertilised eggs are released from the mesenteries to become planktonic; the planulae larvae are supposed to re-enter the coelenterons of the adult where they metamorphose to tentaculate juveniles. Later they are released again to settle and attach. Viviparity in such sessile marine organisms would be ecologically advantageous where suitable settling sites are restricted to narrow vertical limits in the intertidal region, but they are also confined to very few areas of head, stable rock within those vertical limits. Any brooded juvenile or released larva that does not settle near the brooding adult would have an extremely low probability of finding another suitable settling site (Ottaway, 1971).        

Intra-specific aggression: Response in the form of acrorhagial attack where aggression is initiated when the tentacles of two individuals come into contact. The acrorhagi of the "aggressor" were inflated and contraction of the body wall column brought the inflated acrorhagi into contact with the "victim's" column. Acrorhagial nematocysts were discharged into the epidermis (Bonnin, 1964), commonly referred to as acrorhagial peeling which results in 'localised ectodermal necrosis' (Ottoway, 1978). Aggressive interactions between adult A. tenebrosa were thought to be consequences of competition over space on inter tidal substrates (Bigger, 1982). Ayers, 1982 discovered that the acrorhagial response is specific and directed particularly only at genetically dissimilar individuals. They respond aggressively towards both adult and juvenile non- clonemates but not towards their own clonemates . The inflated acrorhagi of stimulated individuals peel upon contact with a non- clonemate but did not display any response when in contact with a clonemate, indicating an ability of clonal recognition upon tentacular contact. Juvenile recruitment rates are exceeding low because they are subjected to various hostile environmental conditions such as desiccation so recruitment is most preferred in sheltered areas. However, these areas are usually occupied by adult individuals in dense concentrations hence inter- clonal aggressions are especially significant in establishing and maintaining space to facilitate the recruitment of juvenile clonemates since brooded juveniles usually settle within a few centimetres of their brooding parent (Ottaway, 1979b). Therefore, it can be assumed that only clonemates can live within a clonal territory (Ayers, 1982).                  

Locomotion: Pedal locomotion was not commonly observed in the population although it has been known to occur. Movement is usually slow and imperceptible and occurs by a slow muscular contraction of the pedal disc. They detach their pedal disc from the surface of the substrate and shift by inchworm- like crawling.  Movement was observed to have occurred in the following events: Physical injury induced by moving objects such as rocks or stones. Unfavorable environmental conditions such as desiccation in which A. tenebrosa moved further down the shore, into the waters. Biological interference: Crushing or crowding of A. tenebrosa, especially of the juveniles were followed by small, rapid moves away from the source of irritation. Injury sustained from intraspecific aggression, usually during an acrorhagial attack where the wounded anemone moves away from the aggressor (Ottaway, 1978). Locomotion can be classified into two main types, large directional locomotion which occurs in events of sustained injury, repeated desiccation and biological disturbance from other animals or short sporadic movements which the anemone displays when placed in a new environment, until it settles down on a suitable area of the substrate.   


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