Beadlet Anenome ( Actinia equina )

/ / Marine Inverts

Description

Actinia equina has a smooth body (called a column) with up to 192 tentacles arranged in 6 circles. The tentacles are retracted and the anemone looks like a blob of jelly when disturbed or when it is exposed to air during low tide. A. equina is usually bright red with blue spots around the inside of the column but can also be brown, orange or green. The blue spots are called acrorhagi and contain stinging cells (called nematocysts) (1). The height of the anemone can be up to 7 cm tall and the base can be up to 6 cm in diameter often outlined with a blue ring (2). A. equina is one of 14 Actinia species but A. equina is the only species found in the Mediterranean (3).

Habitat

A. equina is often found attached to hard substrates in shallow water down to 8 m in exposed and sheltered conditions (4). They are well adapted to live in areas with extreme temperature and salinity fluctuations and can tolerate high temperatures and desiccation (loss of moisture) (5).

Life Cycle

A. equina can reproduce sexually or asexually and is the only anemone species that is viviparous (brood their young). In sexual reproduction, the egg is fertilised by sperm in the gastric cavity and develops there until it is ready to be released (3).

Asexual reproduction involves the release of planktonic young into the ocean which then enter the gastric cavity of another anemone (male or female) where it further develops and is then released to settle on the substrate (3).

Distribution

A. equina is found in the Mediterranean Sea, around the coasts of Britain, the Canary Islands and from the White Sea in Russia to the West coast of Africa (3).

Behaviour

Actinia equina are solitary anemones and show aggressive behaviour towards neighbouring individuals. When their tentacles come into contact, one anemone will sting the other with the nematocysts contained in the acrorhagi which forces the individual to move away (1). Anemones are often thought of as sessile animals but they can move themselves by sliding their base along the substratum.

Food

A. equina are opportunistic omnivorous suspension feeders which have relatively short tentacles and cannot actively search for prey therefore they feed on organisms or detritus that falls onto their oral discs (2). Although their main food source is organic detritus, molluscs and small crustaceans could be a potential food source of A. equina (6).

Conservation status

Not evaluated under IUCN Redlist (7).

References

Description written by Jennifer Lam (2009)

(1) MarLIN. 2008. Actinia equina. Beadlet anemone. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme. MarLIN, Marine Biological Association of the United Kingdom. [Online]. [Cited: 10 June 2009.] http://www.marlin.ac.uk/speciesinformation.php?speciesID=2359

(2) Chomsky, O., Kamenir, Y., Hyams, M., Dubinsky, Z., Chadwick-Furman, N.E. 2004. Effects of feeding regime on growth rate in the Mediterranean Sea anemone Actinia equina (Linnaeus). Journal of Experimental Marine Biology and Ecology, 299. pp. 217-229.

(3) Terrell, D. 2003. Actinia equina. Animal Diversity Web. [Online] [Cited: 11 June 2009.]  http://animaldiversity.ummz.umich.edu/site/accounts/information/Actinia_equina.html

(4) Wirtz, P., Debelius, H. 2003. Mediterranean and Atlantic Invertebrate Guide. Hackenheim, Germany: ConchBooks, p. 46.

(5) Hayward, P., Nelson-Smith, T., Shields, C. 1996. Sea Shore of Britain and Europe.  London, UK: HarperCollins Publishers, p. 68.

(6) Chintiroglou, Ch., Koukouras, A. 1992. The feeding habits of three Mediterranean sea anemone species, Anemonia viridis (Forskal), Actinia equina (Linnaeus) and Cereus pedunculatus (Pennant). Helgolander Meeresuntersuchungen, 46. pp. 53-68.

(7) IUCN. 2009. IUCN Red List. IUCN Red List. [Online] [Cited: 11 June 2009.] http://www.iucnredlist.org.