Pupilla (Pupilla) muscorum (Linnaeus, 1758)
- Turbo muscorum Linnaeus 1758: 767.
Identification. Shell subcylindrical to ovate. Spire tall, with convex sides, apex blunt rounded. Whorls ca 6, flatly rounded-convex. Periphery medial. Suture deep. Protoconch microscopically granular. Teleoconch with low, rounded, unequal colabral wrinkles. Aperture subovate, edentulous or with low parietal tubercle and rarely with a columellar denticle; aperture height ≈ width. Adult lip rather thickened within, expanded. Last whorl constricted next to adult lip; generally with a pale crest behind. Umbilicus narrow. Shell with slight lustre; semi-transparent to opaque; pale grey-brown to orange-brown (often eroded); lip creamy white but orange-brown behind; crest cream-white. Height to 3–4 mm (higher than wide).
Animal pale grey with head and tentacles darker.
The development of the whitish crest, as well as the apertural dentition, shows considerable variation. Both taller, cylindrical shells and shorter, ovate shells occur together in populations. The common form in southern Ontario has only the parietal denticle present, but other forms are also present including those that lack denticles altogether or with various combinations of a parietal, palatal or columellar denticles.
Habitat. A calciphile, in mesic and xeric, open habitats. Gregarious in disturbed habitats including roadsides, embankments, vacant lots, waste ground, old quarries, fields, concrete culverts; also, beach dunes, sandy savannas, and cliffs. In southern Ontario, shell often in great abundance in stream drift. Under debris and rubbish, rocks, dead wood, and dead vegetation, and on concrete structures and rubble.
Canadian range. Introduced to southern Ontario and southern Quebec, New Brunswick, Nova Scotia, and Newfoundland. Until recently not considered introduced (Nekola et al. 2015).
Etymology. Latin, “inhabiting mosses”.
Remarks. Nekola et al. (2015) revised the taxonomy of most members of Pupilla using molecular analyses and conchological characters and showed that Pupilla from boreal North America are not this species but other, native species. They regarded North American populations of P. muscorum to represent an old introduction of this European species. Pilsbry (1948) distinguished one Pleistocene subspecies, not from Canada, that seems unlikely to be directly related P. muscorum as it now is understood. Therefore, no subspecies are used here.
- Linnaeus C (1758) Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata. Laurentii Salvii, Holmiæ,  + 824 pp.
- Nekola JC, Coles BF, Horsák M (2015) Species assignment in Pupilla (Gastropoda: Pulmonata: Pupillidae): integration of DNA-sequence data and conchology. Journal of Molluscan Studies 81: 196–216.
- Pilsbry HA (1948) Land Mollusca of North America (north of Mexico), 2(2). The Academy of Natural Sciences of Philadelphia, Monographs 3: i–xlvii + 521–1113 pp.