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Limacina (Limacina) helicina (Phipps, 1774) subsp. helicina (Phipps, 1774) forma helicina (Phipps, 1774)

Overview

This is a small, shelled, pelagic thecosomatous pteropod with a left coiled shell, 0.8 cm in diameter. The spire is not very depressed. It has about 5 to 6 colourless, transparent whorls. There is an umbilical keel. Transverse striae are present. It is found in colder waters of the N-Atlantic Ocean where it feeds on phytoplankton and it is a mucus feeder (Limacina h.h. helicina shell and wings).

Taxonomic Description

The relatively small shell, composed of 5-6 whorls, is moderately highly spired, the aperture is higher than wide. The shell is completely transparent but the green and brown or purple colour of the body can be seen through the shell (Limacina h.h. helicina). The columella is only faintly curved and bends over. The umbilicus is moderately wide with a keel surrounding it in older specimens. The shell shows clear, transverse striation. The last whorl is much larger than the preceding ones together, but it is not as enormous as in the deep-sea species Limacina helicoides. The operculum is thrown off in older specimens, the nucleus is very eccentric, the number of whorls is 2-3. The wings show a protrusion at the anterior border (Limacina h.h. helicina soft parts). The dorsal tentacles are unequally shaped. A sheet surrounds the right tentacle. The radula formula is 1-1-1 and there are 8-10 transverse rows of teeth.
Shell measurements: height to 6 mm, diameter to 8 mm and height/diameter ratio 0.75.

Juveniles

The juveniles have a small left coiled shell. A special description is not available.

Reproduction

This form is a protandric hermaphrodite and uses spermatophores for sperm transfer. Reproduction occurs in winter and spring, triggered by phytoplankton blooms. There is no brood protection. Eggs are placed in an undulating order in ribbons. Reproduction in this forma is well known. In the area of Igloolik Is, juveniles are found in November, December, June, July and August, while in these months adults are not present. Reproduction starts in winter and continues during spring. This also occurs in the entire East Greenland population, where growth appears to parallel the amount of phytoplankton present.

Ecology

This form is phytophagous and epipelagic. It forms the main food of the gymnosomatous Clione limacina. Whales and seals, also Phoca hispida, are also important predators, while the arctic rorquals use this forma as an important food source. Its temperature range is -0.4° C to +4.0° C, and infrequently up to 7° C. The salinity of the environment is mostly below 34.0°/oo S.

Distribution

The forma helicina is restricted to the N-Atlantic Ocean. The forma helicina is found in Baffin Bay, Hudson Bay, Davis Strait and as far south as 35°N in the Labrador area. In the E-Atlantic near Spitsbergen, the warmer Gulf Stream presses the forma as far north as 75°N. Along the Norwegian Coast the forma is found more southwards, to 63°N. In the Arctic Sea it is found between 90°W and 90°E, which demonstrates its Atlantic-Subarctic character see the Limacina h.h. helicina map.

Types

Clio helicina Phipps, 1774: 195.
The types are probably lost.

Limacina helicina helicina helicina