Moss Chrysalis Snail

Pupilla muscorum, commonly known as the Moss Chrysalis snail^[1] or widespread column,^[4] is a species of minute air-breathing land snail, a terrestrial pulmonate gastropod mollusk or micromollusk in the family Pupillidae.

Taxonomy

A variety Pupilla muscorum var. pratensis Clessin, 1871 considered as ecophenotype of Pupilla muscorum was elevated to its species level Pupilla pratensis in 2009.^[5]

Description

The shell is usually light brown, varies from reddish brown to horny grey, weakly striated or almost smooth, 5–6.5 weakly convex whorls, suture not very deep (deep suture is presented in Pupilla sterrii – see picture below), aperture usually with well-developed lip, cervical callus strongly developed, like a dam, parietal tooth usually present, palatal tooth sometimes too.^[3]

Pupilla muscorum differs from Pupilla pratensis with which it lives sympatrically, in its thicker, smaller and more slender shell, lighter and more variable colour and stronger apertural lip.^[3]

The animal of Pupilla muscorum is small, elliptical, dark with lighter sides and foot, upper tentacles not very long, lower tentacles very short.^[3]

Extant populations of P. muscorum are practically identical in shape to their ancestors, indicating that the have tracked their ecological niches over time.^[6]

The height of the shell is 3.0–4.0 mm. The width of the shell is 1.65–1.75 mm (shell diameter does not vary much).^[3]

Photo of the shell Pupilla sterrii with deep sutures

Drawing of the shell – typical view of Pupilla muscorum with shallow sutures.

Distribution

This species of land snail occurs in the Northern Hemisphere including almost all of Europe. It is recorded as present in countries and islands including:

• Great Britain. It is threatened by disturbance due to intensification of land use of old calcareous grasslands in Britain.^[3]
• Ireland
• lower concern in Austria. Vulnerable in Vorarlberg.^[3]
• lower concern in Germany, decreasing (4R) in Bavaria.^[3]
• Czech Republic^[7]
• Slovakia^[7]
• Ukraine^[8] and Crimea^[9]
• Pakistan^[10]
• Michigan, USA^[11]
• Utah, USA^[4]
• Vermont, USA^[12]

Ecology

Pupilla muscorum lives in dry meadows, sand dunes, in open and sunny habitats.^[3] Calciphile.^[3] In Portugal it is found under stones, dead leaves and in mosses.^[3] In Britain it is frequent in sheep-grazed calcareous grasslands.^[3] In the Alps in up to 2400 m, in Bulgaria 1200 m.^[3]

Ovoviviparous, the species is able to hibernate with its eggs, and can then release eggs with partly grown embryos during more favourable seasons.^[3]

References

This article incorporates public domain text from the reference.^[3]