Carychium occidentale

Carychium occidentale Pilsbry, 1891
Western Thorn


Phylum Mollusca > Class Gastropoda > Clade Heterobranchia > Informal Group Pulmonata > Clade Eupulmonata > Superfamily Ellobioidea > Family Ellobiidae > Subfamily Carychiinae


  • Carychium exiguum var. occidentalis [sic] Pilsbry 1891: 109. Portland, Oregon, U.S.A. Nomen correctum, occidentale.
  • Carychium magnificum Hanna 1923: 51, f. 1. Union Bay, Vancouver Island, British Columbia, Canada.
Carychium occidentale

Carychium occidentale

Diagnosis and description

Diagnosis: Among Canadian species of Carychium, this is the largest species (mature H up to 2.7 mm), further distinguished by its clearly tapering spire, weakly sculptured shell, and thin, but expanded, palatal lip.

Shell: Maximum mature h: 2.0–2.7 mm; growth determinate; rather broadly fusiform, thin-shelled; translucent. Whorls: ca 5–5½; evenly increasing in width; spire whorls convex. Spire: elongate; sides usually ± straight; apex bluntly rounded. Suture: deep. Last whorl: not descending to the peristome; no crest. Protoconch: smooth. Teleoconch sculpture: smooth, with weak colabral striae. Periostracum: inconspicuous. Aperture: subovate; ca 1/3 of H. Peristome: incomplete. Apertural dentition: 1 (larger) parietal lamella that continues internally around columella a smooth curve; 1 weakly formed lamella at base of columella that may be lacking. Palatal 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. Colour (periostracum): colourless or white; with a silken sheen.

Animal: Body white with dark eyespots.

Anatomy: Unknown.

Range and habitat

Global range: Northern Vancouver Island, British Columbia (Forsyth 2004), south to northern California where it occurs in the coastal counties of Del Norte, Humboldt and Mendocino (Roth & Sadeghian 2006); east through northern Washington to Idaho (Frest & Johannes 2001).

Canadian range: Currently known in British Columbia from the west side of the Coast and Cascade ranges, on Vancouver Island, and on other islands along the south coast, it should be expected in the wet southern interior parts of the province. North along the coast at least to Menzies Bay (50°10´ N, RGF coll.), eastern Vancouver Island. Distribution is sporadic.

Ecozone: Pacific Maritime; possible for the southern Montane Cordillera.

Habitat: In relatively undisturbed low elevation (≤ 80 m a.s.l.) deciduous and mixedwood forests. Bigleaf Maples (Acer macrophyllum) are usually present. Colonies are found sporadically in deep litter areas, and nearly always in moist hollows, near seeps or along riparian zones.


The biology of this species is unknown.


Early records of Carychium exiguum from British Columbia (Taylor 1889, 1891, 1895, La Rocque 1953) must have been misidentifications and instead refer to C. occidentale which had not yet, or had only just been described. Pilsbry (1891) first recognized the west coast form as distinct, describing it as a subspecies of C. exiguum, but within a few years, he raised it to a species (1894). As originally written, the spelling of the species epithet was “occidentalis, but following the rules of Latin, the ending was changed to the neuter; hence, occidentale. Hanna (1923) described Carychium magnificum from Vancouver Island, thinking wrongly that his material belonged to a larger-shelled species than C. occidentale. However, Pilsbry (1948: 1061) synonymized the two taxa, noting that “though the types of C. occidentale were smaller, it often reaches the size given for C. magnificum.

Etymology: Genus, from the Greek, karyx (κάρυξ), “a herald”, signifying the ancient use of a shell as a trumpet. The gender is neuter.Species epithet, Latin, “western”.


Species bibliography at
Species account, map and photo gallery at

Literature Cited

  • Forsyth, R.G. 2004. Land Snails of British Columbia, Royal BC Museum Handbook. Victoria: Royal British Columbia Museum. iv + 188 p., [8] pl.
  • Frest, T.J., and Johannes, E.S. “2000” [2001]. An annotated checklist of Idaho land and freshwater mollusks. Journal of the Idaho Academy of Sciences 36 (2): 1–51.
  • Hanna, G.D. 1923. A new species of Carychium from Vancouver Island, British Columbia. proceedings of the California Academy of Sciences (4)12 (5): 51–53.
  • La Rocque, A. 1953. Catalogue of the Recent Mollusca of Canada. National Museum of Canada, Bulletin 129: x + 406 p.
  • Pilsbry, H.A. 1891. Forms of American Carychium. The Nautilus 4 (10): 109–110.
  • Pilsbry, H.A. 1894. The American species of Carychium. The Nautilus 6 (6): 61–63.
    Pilsbry, H.A. 1948. Land Mollusca of North America (north of Mexico). Volume 2, Part 2. Academy of Natural Sciences of Philadelphia, Monograph 3: i–xlvii + 521–1113.
  • Roth, B., and Sadeghian, P.S. 2006. Checklist of the land snails and slugs of California. Second edition. Santa Barbara Museum of Natural History Contributions in Science 3: 82 p.
  • Taylor, G.W. 1889. The land shells of Vancouver Island. The Ottawa Naturalist 3: 84–94.
  • Taylor, G.W. 1891. Land shells of Vancouver Island. The Nautilus 5 (8): 91–92.
    Taylor, G.W. 1895. Preliminary catalogue of the marine Mollusca of the Pacific coast of Canada with notes upon their distribution. Transactions of the Royal Society of Canada (2) 1 (4): 17–100.