View source for Biology:Allantactis

{{Short description|Genus of sea anemones}}
{{Speciesbox
</ref>
| taxon = Allantactis parasitica
| authority = Danielssen, 1890<ref name=Danielssen/>
| synonyms = * ''Calliactis kroeyeri''<small> Danielssen, 1890</small>
* ''Calliactis kroyeri''<small> Danielssen, 1890</small>
* ''Calliactis krøyeri''<small> Danielssen, 1890</small>
| synonyms_ref = <ref name=WoRMS>{{cite WoRMS |author=Fautin, Daphne |year=2015 |title=''Allantactis parasitica'' Danielssen, 1890 |id=100933 |accessdate=28 June 2017|db=}}</ref> 
}}

'''''Allantactis''''' is a [[Biology:Monotypic taxon|monotypic]] [[Biology:Genus|genus]] of [[Biology:Sea anemone|sea anemone]]s, and '''''Allantactis parasitica''''' is the only [[Biology:Species|species]] in the genus.<ref>{{cite WoRMS |author=Fautin, Daphne |year=2015 |title=''Allantactis'' |id=100752 |accessdate=28 June 2017|db=}}</ref> This sea anemone lives at [[Earth:Bathyal zone|bathyal depths]] in the North Atlantic Ocean and has a [[Earth:Symbiosis|symbiotic relationship]] with a [[Biology:Gastropoda|gastropod mollusc]].

==Description==
''A. parasitica'' has a strong base and a smooth column with thick walls and no cuticle or perforations of the body wall that are termed ''cinclides''. The margin is distinct and the sphincter powerful. The [[Biology:Tentacle|tentacle]]s are fairly short and arranged in whorls of six, there being a maximum of 96. The oral disc has a central mouth with two broad [[Biology:Siphonoglyph|siphonoglyph]]s. The six pairs of [[Biology:Mesentery (zoology)#Cnidaria|mesenteries]] are complete, in that their sheetlike membranes join the gastrodermis of the body wall with that of the pharynx, and are sterile, in that they do not bear gonads. The nematocysts consist of a mixture of spirocysts, basitrichs and microbasic p-mastigophors.<ref>{{cite web |url=http://tolweb.org/Allantactis_parasitica/18124 |title=''Allantactis parasitica'' |publisher=Tolweb |accessdate=28 June 2017}}</ref>

==Ecology==
The species lives on the abyssal seabed of the North Atlantic at depths of between {{convert|725|and|1100|m|ft|-2|abbr=on}}. Although sometimes living attached to a pebble or empty shell, it prefers to attach to the shell of a living gastropod mollusc when available. Sea anemone larvae settling on the seabed do so preferentially on any gastropods that are present, and where the larvae settle onto mud, the presence of gastropods nearby stimulates them to move towards and onto the molluscs. Sometimes as many as six anemones can be found crowded onto the shell of a single living gastropod.<ref name=Merciera>{{cite journal |author=Merciera, Annie |author2=Hamel, Jean-François |year=2008 |title=Nature and role of newly described symbiotic associations between a sea anemone and gastropods at bathyal depths in the NW Atlantic |journal=Journal of Experimental Marine Biology and Ecology |volume=358 |issue=1 |pages=57–69 |doi=10.1016/j.jembe.2008.01.011 }}</ref>

Gastropods with one or two sea anemone on their shells were found to have greater feeding success and more varied stomach contents than those with either no epibionts, or with three or more. The sea anemones also benefited from the mutualism because of the longer time spent in food-rich areas in the deep sea floor, a place where food resources are limited.<ref>{{cite book|title=Issues in Ecosystem Ecology|edition=2012|url=https://books.google.com/books?id=oQ5s7gUVDKgC&pg=PA97 |year=2013|publisher=ScholarlyEditions |isbn=978-1-4816-4649-9 |pages=97–28}}</ref>

The chief [[Earth:Predation|predator]] of gastropods at these depths in the North Atlantic is the starfish ''Leptasterias polaris''. Researchers found that starfish avoided molluscs with anemones on their shells, and that molluscs relied on the presence of their [[Biology:Epibiont|epibiont]]s and did not take evasive action when they encountered the starfish. If their attached anemones were removed, they lost the protection that their toxin-producing nematocysts provided, and were attacked. The sea anemone gained advantage from being an epibiont as it is itself sometimes attacked by the starfish ''Crossaster papposus'', but was able to escape from this predator when attached to a living gastropod mollusc.<ref name=Merciera/>

Despite living at bathyal depths where no light penetrates, ''A. parasitica'' is one of a number of deep sea species that show synchronisation in the release of eggs and sperm to the [[Astronomy:Lunar phase|phases of the moon]].<ref>{{cite book|author1=Numata, Hideharu|author2=Helm, Barbara|title=Annual, Lunar, and Tidal Clocks: Patterns and Mechanisms of Nature's Enigmatic Rhythms|url=https://books.google.com/books?id=j_lNBgAAQBAJ&pg=PA109 |year=2015 |publisher=Springer |isbn=978-4-431-55261-1 |pages=109–111}}</ref>

==References==
{{Reflist|30em}}
{{Taxonbar|from=Q2013147|from2=Q21445761}}

[[Category:Hormathiidae]]
[[Category:Monotypic cnidarian genera]]
[[Category:Hexacorallia genera]]

{{Sourceattribution|Allantactis}}