Carychium exiguum

Carychium exiguum (Say, 1822)
Obese Thorn

  • Pupa exigua Say 1822: 375.
  • Carychium existelium Bourguignat 1857: 220.
  • Carychium euphaeum Bourguignat 1857: 221.
Carychium exiguum
Carychium exiguum; Bellwood Conservation Area, Lake Bellwood, West Garafraxa, Wellington County, Ontario (RGF 08.160.7558), height 2.05 mm.

Identification. Shell fusiform. Spire elongate, with convex sides. Apex bluntly pointed. Whorls ca 5, convex. Suture rather well-indented. Protoconch smooth. Teleoconch with weak incremental striae initially, more-or-less regular, colabral striae on last two whorls. Aperture subovate, higher than wide, height ca 30% of shell height; 1 parietal lamella, continuing internally around columella in an undulating spiral; 1 smaller lamella at base of columella. Adult lip expanded, a little recurved, thickened on inner side, especially medially on palatal lip. Belly of the last whorl projected beyond the plane of peristome. Chink-like “false umbilicus” against base of last whorl. Shell translucent, colourless when fresh, opaque, and white when weathered. Shell 1.7 mm high (higher than wide).

Animal white, with small black eyespots at bases of sensory tentacles. Anterior portion of foot bilobed.

This species can be recognized by the bulging last whorl, medium-sized shell for a Carychium, only lightly striate sculpture, and thickened palatal lip. It differs from C. minimum by having one more whorl and a taller form. The penultimate whorl bulges beyond the profile of the palatal lip when viewed from the side. The internal lamella is undulate.

Habitat. Floodplain woods, marshy edges of streams, swamps, marshes and other water bodies, wooded rocky outcrops, alvars, and grasslands. A calciphile. In moist leaf litter and rotting vegetation, and under fallen bark and other woody debris. In damp pockets in depressions along forest streams. Carychium exiguum and C. exile are sometimes sympatric. (Harry 1952, La Rocque 1970, Nekola 2004, unpubl. data)

Global range. Canada and south in the USA to Alabama, Colorado, and southwestern New Mexico (Pilsbry 1948). Hubricht (1985) recorded this species mostly in the northern US states, from Maine west to South Dakota, Colorado; collections from Texas, Oklahoma, Louisiana, and Mississippi were believed to be based on fossil material (Hubricht 1985). In Mexico, south to at least Nuevo León (Naranjo-García & Fahy 2010).

Canadian range. Central Alberta east through Ontario to the Maritime Provinces and Newfoundland.

In Ontario, from the lower Great Lakes region north to Onakawana, near James Bay, and northwest at least as far as Huron Bay, Thunder Bay (Oughton 1948) and into Manitoba (Christy 1885, Dall 1905).

Specimens reported as Carychium exile from east of Darwell, Alberta (Van Es & Boag 1981; CMNML 86010) are instead C. exiguum; however, C. exiguum was also reported from Alberta by Harris & Pip (1973) (unconfirmed) and was collected at Smoky Lake by T. Neckheim (pers. comm. 2010).

Early reports of this species from Vancouver Island (e.g. Taylor 1889), and repeated in subsequent literature, most probably refer to C. occidentale instead; C. exiguum has not been found in British Columbia in recent times (Forsyth 2004).

Etymology. Latin exiguus, “short” or “small”.

References

  • Bourguignat JR (1857) Aménités Malacologiques. LXIV. Du genre Carychium. Révue et Magasin de Zoologie pure et appliquée (2e série) 9: 209–232.
  • Christy RM (1885) Notes on the land and fresh-water Mollusca of Manitoba. The Journal of Conchology 4: 339–349.
  • Dall WH (1905) Land and fresh water mollusks. Doubleday, Page and Co., New York, 1–171, pls 1, 2.
  • Forsyth RG (2004) Land Snails of British Columbia. Royal British Columbia Museum, Victoria, iv + 188 + [8] pp
  • Harris SA, Pip E (1973) Molluscs as indicators of late- and post-glacial climatic history in Alberta. Canadian Journal of Zoology 51: 209–215.
  • Hubricht L (1985) The distributions of the native land mollusks of the eastern United States. Fieldiana, Zoology (New Series) 24: i–viii, 1–191.
  • 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.
  • Say T (1822) Description of univalve terrestrial and fluviatile shells of the United States. Journal of the Academy of Natural Sciences of Philadelphia 2: 370–381.
  • Taylor GW (1889) The land shells of Vancouver Island. The Ottawa Naturalist 3: 84–94.
  • Van Es J, Boag DA (1981) Terrestrial molluscs of central Alberta. The Canadian Field-Naturalist 95: 75–79.