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''Limacina helicina'' is a species of small swimming predatory sea snail in the family Limacinidae, which belong to the group commonly known as sea butterflies (Thecosomata).〔Bouchet P. & Gofas S. (2011). ''Limacina helicina'' (Phipps, 1774). Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=140223 on 2011-02-07〕〔 ''Limacina helicina'' is a keystone species of mesozooplankton in Arctic pelagic ecosystems.〔〔〔 The first written record of this species was by Friderich Martens from Spitsbergen in 1675.〔 Martens F. (1675). (''Spitzbergische oder Groenlandische Reise Beschreibung gethan im Jahr 1671'' ). Schultzen, Hamburg. page 110〕〔 ''Limacina helicina'' was also observed during an 1773 expedition to the Arctic led by Constantine John Phipps on the ships HMS ''Racehorse'' and on HMS ''Carcass'' and the species was described one year later, in 1774.〔 ''Limacina helicina'' is the type species of the genus ''Limacina''.〔Janssen A. W. (2007). "Holoplanktonic Mollusca (Gastropoda: Pterotracheoidea, Janthinoidea, Thecosomata and Gymnosomata) from the Pliocene of Pangasinan (Luzon, Philippines)". ''Scripta Geologica'' 137 http://www.scriptageologica.nl/07/nr135/a02〕 In contrast to the traditional view, it was shown in 2010 that the distribution of this species is not bipolar; Arctic and Antarctic individuals belong to two genetically distinct species: ''Limacina helicina'' in the Arctic, and ''Limacina antarctica'' in the Antarctic.〔〔 == Subspecies == * ''Limacina helicina helicina'' (Phipps, 1774)〔Bouchet, P.; Gofas, S. (2011). Limacina helicina (Phipps, 1774). Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=140223 on 2011-01-29〕 * ''Limacina helicina acuta'' Van Der Spoel, 1967〔Spoel S. van der (1967). "Euthecosomata, a group with remarkable developmental stages (Gastropoda, Pteropoda)". ''J. Noorduyn and Zn, Gorinchem'', 375 pp.〕 * ''Limacina helicina ochotensis'' Shkoldina, 1999〔 * ''Limacina helicina pacifica'' Dall, 1871〔Dall W. H. (1871). "Descriptions of sixty new forms of mollusks from the west coast of North America and the north Pacific Ocean, with notes on others already described". ''American Journal of Conchology'' 7(2): (93 )-160, plates (13 )-16. (Pages 138-139 ).〕 ''Limacina helicina'' has been recognised as a species complex comprising two sub-species and at least five forms.〔 In addition, the taxonomic category “forma” has been applied to designate at least three morphotypes of ''Limacina helicina helicina'' (''acuta'', ''helicina'' and ''pacifica'') and two morphotypes of ''Limacina helicina antarctica'' (''antarctica'' and ''rangi'').〔 It is also known as ''Limacina helicina rangii'' (d'Orbigny, 1835).〔 These forms typically have different geographical ranges, but it remains unclear as to whether forms represent morphological responses to different environmental conditions or are indeed taxonomically distinct, and if the latter, their level of taxonomic separation.〔 However, at the species level the geographical distribution is considered to be bipolar, as it occurs in both the Arctic and Antarctic oceans.〔 Remigio and Hebert (2003) provided initial evidence for the genetic separation of ''Limacina helicina helicina'' and ''Limacina helicina antarctica''.〔 Hunt et al. (2010)〔 have quantified genetic distance within these taxa. Hunt 2010 found a 33.56% difference in cytochrome c oxidase subunit I (COI) gene sequences between the "''Limacina helicina''" which were collected from the Arctic and the Antarctic oceans.〔 This degree of separation is sufficient for ordinal level taxonomic separation in other organisms, and provides strong evidence for the Arctic and Antarctic populations of ''Limacina helicina'' differing at least at the species level.〔 Subspecies ''Limacina helicina antarctica'' Woodward, 1854 can be considered as a separate species ''Limacina antarctica'' Woodward, 1854.〔 A conservative divergence time estimate of 31 Ma (95% HPD interval 12–53 Ma) for Arctic and Antarctic taxa, indicates that they have undergone rapid independent evolution since the establishment of cold water provinces in the early Oligocene.〔 Also there is different structure of the shell between ''Limacina helicina'' and ''Limacina antarctica''. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Limacina helicina」の詳細全文を読む スポンサード リンク
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