Mesodon sayanus

Mesodon (Appalachina) sayanus (Pilsbry in Pilsbry & Ferriss, 1906)
Spike-lip Crater

  • Helix diodonta Say 1824: 257, pl. 15, fig. 4, nomen obsoletum (but not preoccupied).
  • Helix sayii A. Binney 1840 (1837–1841): 379, pl. 16, nomen novum pro Helix diodonta Say, 1824.
  • Polygyra sayana Pilsbry in Pilsbry & Ferriss 1906: 127, nomen novum pro Helix sayii A. Binney, 1840 and Helix diodonta Say, 1824.
Appalachina sayana, Aylmer, Gatineau, Québec (rgf 02.008.4954), w: 22.1 mm.
Appalachina sayana; Aylmer, Gatineau, Québec (RGF 02.008.4954), width 22.1 mm.

Identification. Shell depressed-globose. Spire moderately elevated, conical. Whorls ca 5, convex., slightly shouldered. Periphery rounded, medial on last whorl. Suture deep. Last whorl descending only a little near peristome; constriction of whorl behind the basopalatal lip moderate; crest negligible. Protoconch smooth. Teleoconch with fine, equal, evenly space axial threads and microscopic spiral striae. Periostracum non-hirsute. Aperture subrotund, height and width about equal. Apertural dentition: 1 small, tubercle-like denticle on basocolumellar lip. Palatal and basocolumellar lip: rather narrowly expanded, thin-edged, and slightly recurved. Peristome, viewed from side, prosocline, nearly straight. Parietal callus glazed, transparent, inconspicuous. Umbilicus ca 1/6 of shell width, scarcely overhung by the columellar lip. Shell rather thin, nearly opaque; pale yellow-brown, with a silky lustre; expanded lip and parietal denticle white. Shell 19–22 wide (wider than high).

The combination of a rather large, lightweight shell having an open umbilicus, small basocolumellar and parietal denticles, and surface sculpture of fine, evenly spaced axial threads serve to distinguish this species from all other Eastern Canadian polygyrids.

Animal light reddish-brown, with smoky grey tentacles and black eyes (Say 1824).

Habitat. In forests, in rocky, shaded, mesic areas, including on wooded alvars (such as in Gatineau, Quebec). In leaf litter and around logs.

Biology. Latchford (1885) inferred that this species reaches maturity in its second year.

Global range. Eastern North America but mainly Appalachian; Southern Ontario, southern Quebec to New Brunswick and Nova Scotia, south through Maine to Tennessee and west to Michigan (Pilsbry 1940).

Canadian range. Ontario north to Algonquin Park and mostly north and east of Hamilton and Toronto (Oughton 1948); probably rare in the western part of its range in Ontario. Around 1890, it was recorded as “very local” at Hamilton (Hanham 1890). Oughton (1948) knew of no fresh shells from counties bordering Lake Erie although the species was found in First Nations middens near Aylmer, Elgin County; he speculated, probably correctly, that this species had been locally extirpated with removal of native forest. Gatineau region of Quebec and along the St Lawrence River into New Brunswick, where records are scattered and rare. In Nova Scotia, on the Isthmus of Chignecto and near Windsor (Dimelow 1962).

Etymology. Named for Thomas Say (1787–1834), an early American naturalist, malacologist, entomologist, and carcinologist, born in Philadelphia, Pennsylvania.

Remarks. Pilsbry (1940) credited the authorship of Polygyra sayana only to himself, but it was in a publication with dual authorship (Pilsbry & Ferriss 1906), and so the authorship of this species is cited as “Pilsbry in Pilsbry & Ferriss”.

Dourson (2011) described a subspecies from Kentucky, as Appalachina sayana kentucki Dourson, 2011. If subspecies are warranted, Canadian populations would be expected to belong to the nominotypical subspecies, M. sayanus sayanus.