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Limacina (Limacina) retroversa (Fleming, 1823) subsp. australis (Eydoux and Souleyet, 1840)

Overview

This is a small, shelled, pelagic thecosomatous pteropod with a left-coiled shell, 0.2 cm in diameter. The spire is highly coiled. It has more than 6 colourless, transparent whorls. There is no umbilical keel. Transverse striae are present (Limacina r. australis 1). Spiral striation is faint. It is found in colder waters of the southern ocean where it feeds on phytoplankton, it is a mucus feeder.

Taxonomic Description

The shell as is forma balea, coiled higher than in retroversa. The spiral striation is similar to the forma retroversa. The shell aperture is not so very large and not rounded but the relative width is more than in retroversa as is the umbilicus is broader than in the forma retroversa. The wing protrusion is present. The characters overlap those of the formae retroversa and balea and the distribution is the best character of the present forma, but it is not a character indicative for a separate taxon. Variability in this forma is great as seen in the following illustrations (Limacina r. australis, Limacina r. australis 1, Limacina r. australis 2, Limacina r. australis 3).
Shell measurements: height to 2.5 mm, maximum diameter 1.5 mm.

Juveniles

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

Reproduction

The species is a protandric hermaphrodite. The reproduction period begins in spring and at the end of the summer, so that there are two generations each year. The specimens born in spring reproduce in summer, those born in summer reproduce the next spring.

Ecology

The species is phytophagous and epipelagic. The temperature range is 4.4-16.7°C and the salinity range is 33.23-35.73 %o S. Lepas anatifera australis preys on the present species.

Distribution

In the Antarctic Ocean the forma australis is rare the coldest waters but most frequently between 50°S and 60°S. A dubious record is known from 22°N, but as Limacina helicina forma rangi also reaches far north in the Brazil Current, see the Limacina r. australis map. For seasonal differences see Limacina r. australis map 2.

Types

Spirialis australis Eydoux and Souleyet, 1840: 237.
Types could not be found.

Limacina retroversa australis