Family Discidae Thiele, 1931 (1866)
Species in Canada Anguispira (Anguispira) alternata (Say, 1817) Anguispira (Zonodiscus) kochi kochi (L. Pfeiffer, 1846) Anguispira (Zonodiscus) kochi occidentalis (E. von Martens, 1882) Discus (Antediscus) shimekii (Pilsbry, 1890) Discus (Discus) patulus (Deshayes, 1830) Discus (Discus) whitneyi (Newcomb, 1864) Discus (Gonyodiscus) rotundatus (O. F. Müller, 1774)◆ ◆ = introduced
Genus Anguispira Morse, 1864
- Anguispira Morse 1864: 11; type species by monotypy: Helix alternata Say, 1817.
Etymology. Latin: anguis, a snake, + spira, a spiral or coil. The gender is feminine.
Subgenus Anguispira Morse, 1864
Subgenus Zonodiscus Pilsbry, 1948
- Zonodiscus Pilsbry 1948: 591; type species by original designation: Anguispira kochi (L. Pfeiffer, 1846).
There is a single species, Anguispira kochi, which is apparently unique among large and relatively well-known snails in having a remarkably disjunct distribution on a continental scale. The eastern and western populations of Anguispira kochi are separated by over 2,000 km, and while there are no consistent morphological characters known to separate these two taxa (Pilsbry 1948), it seems appropriate to distinguish the two as geographic subspecies, as done by Pilsbry (1948).
Etymology. Greek: zoni, zone or belt, + discos, a disc.
Genus Discus Fitzinger, 1833
- Discus Fitzinger 1833: 99; type species by subsequent designation (Gray 1847: 174, ICZN 1955 Opinion 335): Helix ruderata A. Férussac, 1821.
Four species of Discus occur in Canada, including one of the most ubiquitous and widespread land snails, D. whitneyi, which occurs in every province and territory.
Etymology. Greek: discos, a disc; masculine.
Subgenus Discus Fitzinger, 1833
Subgenus Gonyodiscus Fitzinger, 1833
Gonyodiscus Fitzinger 1833: 98; type species by monotypy: Helix perspectiva Megerle von Mühlfeld, 1818.
Patula Held, 1837 is sometimes used instead as the subgenus for D. rotundatus (e.g., Roth & Sadeghian 2003), but Umiński (1962) considered Patula to be a synonym of Gonyodiscus, which is the classification adopted here. Earlier, Forcart (1957) concluded that both Patula and Gonyodiscus are synonyms to Discus, which is followed by Schileyko (2002).
Etymology. Greek: gonia, angle + discos, a disc.
Subgenus Antediscus H. B. Baker in Pilsbry, 1948
- Antediscus H. B. Baker in Pilsbry 1948: 600, 617; type species by monotypy: Zonites shimekii Pilsbry, 1890 (according to Schileyko 2002).
Pilsbry (1948) published this name as a “section”, attributing authorship to Baker, and subsequent authors (e.g., Schileyko 2002) have treated it as a subgenus of Discus. It seems weakly defined.
Etymology. Latin: ante, before + Greek: discos, a disc.
Key to Species of Discus of Canada
- 1a Shell with reddish spots — D. rotundatus
- 1b Shell without reddish spots — 2
- 2a Colabral ribs below the periphery interpolated by additional discontinuous ones. Columellar wall usually with a tubercular denticle. Southwestern Ontario only —D. patulus
- 2b Colabral ribs below the periphery not interpolated by additional discontinuous ones, or basal surface quite smooth (ribs few). No denticle on the columellar wall — 3
- 3a Ribs strong on base. Shell usually more reddish than yellowish brown. Periphery rounded to strongly carinate. A widespread species — D. whitneyi
- 3b Ribs noticeably weaker on base than on apical surface. Shell yellowish brown. Periphery rounded. Northern and western — D. shimekii