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Limacina (Limacina) helicina (Phipps, 1774) subsp. antarctica (Woodward, 1854) forma rangi (d'Orbigny, 1836)

Overview

This is a small, shelled, pelagic thecosomatous pteropod with a left-coiled shell, 0.4 cm in diameter. The spire is not strongly depressed. It has about 6 colourless, transparent whorls. There is no umbilical keel. Transverse striae are absent. It is found in colder waters of the southern oceans where it feeds on phytoplankton and it is a mucus feeder (Limacina h.a. rangi 1).

Taxonomic Description

The shell with about 6 whorls, has a higher coil than in the forma antarctica and helicina and it is colourless, transparent. The umbilicus is wide, the umbilical keel and transverse striation are lacking (Limacina h.a. rangi, Limacina h.a. rangi 2). The shell is not smooth as in the forma pacifica, but spiral striation of small dark tubercles covers the surface. In some specimens of the forma antarctica similar striation in spiral direction is found, but it is fainter than in the present forma. The shell aperture is higher than broad. There is no wing protrusion.
Shell measurements: diameter to 3.5 mm, height to 2.0 mm.

Juveniles

The juveniles have a small left coiled shell. Embryonic shell with rough ornamentation of irregularly ramified, flat ridges (Boltovskoy, 1974).

Reproduction

Spawning appears to take place in the Antarctic winter in June, and is thus comparable with that in the forma antarctica, with reproduction occurs in austral winter. It is a protandric hermaphrodite.

Ecology

This form is phytophagous and epipelagic. Temperature range is 7.4-17.4°C and the salinity range is 33.55-36.14 %o S.

Distribution

This forms shows an Antarctic circumglobal pattern. The northern distribution border of the forma rangi, in the Pacific and Indian Ocean coincides with the northern distribution border of the West Wind Drift. The forma is not recorded east of New Zealand, although samples are known from this area. The forma rangi is found in the Falkland and Brazil Current as far north as 10°S, near S-Africa it only reaches north to 30°S, and this suggests a preference for higher temperatures. Curiously, the southern boundary of this forma north of the Weddell Sea bends southwards, see the Limacina h.a. rangi map.

Types

Atlanta rangii d'Orbigny, 1836: 176 (1846) pl. 2, fig. 25-28.
Syntypes: BMNH 1854.12.4.37, 3 complete and 1 damaged spec. badly dissolved (dry collection, original alcohol collection).
Type loc: Atlantic Ocean. Col. CVAM.

Limacina helicina antarctica rangi