Discus rotundatus (Müller 1774) Garden Disc Snail
Superfamily Discoidea - Disc Snails
Family Discidae - Disc Snails
Status: patchily established alien.
AKS 'introduced ms' figures: South Rosedale, Toronto, Ontario, 30 Nov 1953, CMN 91756
AKS APTW p 79., Ontario: York Region: Scarborough: Bluffers Park Western Beach, Frederick W. Schueler 94/035/bj. DET_BY: F.Wayne Grimm.
Description: Shell dextral, 5.5-7.2 mm in diameter, discoidal with a low domed spire and 4.5-6 whorls, a shallow suture, and dull periostracum with clear, numerous, evenly spaced growth lines. The outer edge of the shell is broadly angular, and all the whorls can be seen inside the umbilicus. The colour is dull greyish brown with distinct reddish-brown bands, or ‘flammulae,' at regular intervals.
Animal: Grey to grey-brown, very slow and secretive. This is one of the few introduced land snails that feeds primarily upon litter and soil and is not a pest. As with most stylommatophoran pulmonates it is hermaphroditic and requires cross-fertilisation. It deposits calcareous eggs in groups of1-5.
Native Range: Southern Scandinavia and Northern Scotland to Algeria, and from Spain and Ireland to the Ukraine. (Roth, 1982) It has been introduced to parts of Europe beyond its native range.
Introduced Range: Disturbed areas in Pacific Coastal United States; one record from Esquimalt, BC (1953) and one from Bellingham Washington (2001; Forsyth 2004). In the east, northern New York, Manhattan, Long Island, Massachusetts, Newfoundland, and Ottawa & Toronto, Ontario. Because it moves very cautiously it usually remains in confined colonies where it may become quite numerous.
Similar Species: The native holarctic Discus ruderatus and the northeastern Discus catskillensis are smaller and have no flammulae on the shell; the native D. patulus is larger, more solid, with 7 whorls, and has no bands or flammulae. Western Discus have fewer whorls and lack flammulae.
Ecology: This is one of the few introduced land snails that feeds primarily on litter, and is not a pest.
References: See Pilsbry (1948) V II (2): __ __ ; Kerney & Cameron 1979: 102. Roth 1982.
Account: F. Wayne Grimm ‘Introduced' ms, revised and combined with ‘Land Snails of BC,' FWS, 18 October 2005.
Stage: fairly complete Draft, unreviewed.
Terrestrial Gastropods of Canada: Introduction
Discus rotundatus (Müller 1774) - Garden Disc Snail