Limacina (Limacina) helicina (Phipps, 1774) subsp. helicina (Phipps, 1774) forma acuta Van der Spoel, 1967
Overview
This is a small, shelled, pelagic thecosomatous pteropod with a left-coiled shell, 0.4 cm in diameter. The spire is not much depressed. It has about 6 colourless and transparent whorls. There is no umbilical keel. Transverse striae are present. It is found in colder waters of the southern oceans where it feeds on phytoplankton and it is a mucus feeder (Limacina h.h. acuta).
Taxonomic Description
The small, transparent shell has a higher coil than in the formae helicina and pacifica, the number of whorls is about 6. The shell aperture is higher than wide; the other shell characters are similar to those of helicina and the most prominent feature is the lack of transverse striation. The wing protrusions are present on the anterior border.
Shell measurements are: diameter to 2.5 mm, height/diameter ratio 0.971.
Juveniles
The juveniles have a small left coiled shell. A special description is not available.
Reproduction
This is a protandric hermaphrodite. It uses spermatophores for sperm transfer.
Ecology
This is a phytophage and epipelagic.
Distribution
The forma acuta is restricted to the Pacific, between 40° and 50°N, and off the American West Coast between 30° and 60°N. In the California Current and a part of the Alaska Current, the forma acuta is absent and replaced by the forma pacifica. See the Limacina h.h. acuta map. The forma acuta has its most extensive north-south distribution in the Kuro Shio, Kamchatka and North Pacific Currents, where the forma pacifica is absent. The forma pacifica thus prefers the lower latitudes and acuta the higher ones in the Arctic Transitional Area. The vertical distribution range is at daytime from 0 or 150 to 470 m, and at night from 0 to 300 or 600 m.
Types
Limacina (Limacina) helicina helicina forma acuta (nom. nov. pro var. A) McGowan, 1963: 112, fig. 2A (Limacina h.h. acuta holotype).
Holotype: USNM 665802 (dry collection) Paratypes: USNM 665803, 7 fragments (dry collection) .
Type locality: Monterey. Coll.: DALL.