Carychium occidentale

Carychium occidentale Pilsbry, 1891
Western Thorn

  • Carychium exiguum var. occidentalis [sic; gender not in agreement] Pilsbry 1891: 109.
  • Carychium magnificum Hanna 1923: 51, fig. 1.
Carychium occidentale
Carychium occidentale.

Identification. Shell minute, fusiform, thin-shelled. Spire elongate, sides rather straight. Apex bluntly rounded. Suture deep. Periphery rounded. Protoconch smooth. Teleoconch smoothish, with weak colabral striae. Aperture subovate; ca ⅓ of shell height, with 1 larger parietal lamella that continues internally around columella a smooth curve, 1 weakly formed lamella at base of columella that may be lacking. Lip expanded, edge thin, seldom with a low, medial callus on inside. Peristome, viewed from side: prosocline, not strongly sinuous; belly of last whorl not projecting beyond the plane of peristome. Parietal callus glazed, transparent, inconspicuous. Shell colourless or translucent white; with a silken sheen. Shell 2.0–2.7 mm high (higher than wide).

Animal white with black eyespots.

This is the largest Carychium species in Canada, further distinguished by its clearly tapering spire, weakly sculptured shell, and thin, but expanded, palatal lip.

Habitat. In relatively undisturbed deciduous and mixed lowland (≤80 m a.s.l.) forests; Bigleaf Maples are usually present. In deep litter areas, in hollows, near seeps, and in riparian zones that are perpetually moist, but not overly wet. Colonies are sporadic.

Global range. British Columbia, south to northern California where it occurs in the coastal counties of Del Norte, Humboldt, and Mendocino (Roth and Sadeghian 2003); east through northern Washington to Idaho (Frest and Johannes 2001).

Canadian range. British Columbia: along the coast, south of northern Vancouver Island; expected for wet areas of the south-eastern Interior.

Union Bay, Vancouver Island, is the type locality of C. magnificum, a synonym of C. occidentale.

Etymology. Latin, occidentalis, “western”.

Remarks. Early records of C. exiguum from Vancouver Island (e.g. Taylor 1889), which pre-date the description of C. occidentale, are presumed to be this species.


  • Frest TJ, Johannes EJ (2001) [“2000”] An annotated checklist of Idaho land and freshwater mollusks. Journal of the Idaho Academy of Science 36: 1–51.
  • Hanna GD (1923) A new species of Carychium from Vancouver Island, British Columbia. Proceedings of the California Academy of Sciences (Series IV) 12: 51–53.
  • Pilsbry HA (1891) Forms of American Carychium. The Nautilus 4: 109–110.
  • Roth B, Sadeghian PS (2003) Checklist of the land snails and slugs of California. Santa Barbara Museum of Natural History Contributions in Science 3: 1–81.
  • Taylor GW (1889) The land shells of Vancouver Island. The Ottawa Naturalist 3: 84–94.