Limacina helicina is a species of small swimming planktonic sea snail, in the family Limacinidae. It belongs to the group commonly known as sea butterflies (Thecosomata). 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. Limacina helicina was also observed during a 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. 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) Limacina helicina acuta Van Der Spoel, 1967 Limacina helicina ochotensis Shkoldina, 1999 Limacina helicina pacifica Dall, 1871 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.
Distribution The type locality of Limacina helicina is "Arctic seas". Limacina helicina is the only thecosome pteropod in Arctic waters. The distribution of Limacina helicina is arctic and subarctic (subpolar–polar) especially in the Arctic Ocean and countries include:
Northern Atlantic Ocean between 50 and 60 °N, Norwegian Sea, Faroe Islands, North of Iceland, Spitsbergen Greenland: Denmark Strait and Davis Strait Canada: Anticosti Island, Laurentian Channel, Magdalen Islands, Prince Edward Island, Newfoundland, Strait of Belle Isle. USA: area between Cape Hatteras (North Carolina, USA) and Newfoundland island; from the Gulf of Alaska to Friday Harbor, Washington state Russia: White Sea and Novaya Zemlya, Sea of Okhotsk, Sea of Japan, Bering Sea, Chukchi Sea, Kurile Islands, Commander Islands Japan: off Kasumi, Hyōgo
Description
Limacina helicina has wing-like parapodia which evolved from the original gastropod foot (as is the case in all other pteropods). In this species, the color of the soft parts is dark purple or violet, with paler pellucid (translucent) parapodia.
The shell is sinistral, subglobose, subdiscoidal, hyaline and very thin. The spire is depressed but it can be considered rather high in comparison of other Limacina species. The shell has a wide umbilicus and the aaperture is higher than it is wide. The shell has 5-6 transversally striated whorls and a distinct suture. The last whorl is large and with very obscure keel next to its umbilicus. The width of the shell is 5–10 mm or up to 13 mm. The height of the shell is up to 6 mm (when maximum width was 8 mm).
Adult specimens in the genus Limacina have usually lost the operculum. The radula consist of 10 rows. Each row consist of one central tooth and two lateral teeth. The Digestive system also includes an esophagus, gizzard sac and gut.
Ecology
Habitat
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