Patera - Bladetooth Snails (Family Polygyridae)
Bladetooth snails, along with the Wedge Snails (Xolotrema) are mostly depressed-subglobose with a closed umbilicus. Their general form and minimal apertural teeth separate them from most other depressed-subglobose snails. Xolotrema does have a small palatal tooth that Patera lacks.
There are four species in Indiana - three are the typical form of Patera shell but one, the Proud Globelet Snail (Patera pennsylvanica) is more Mesodon-globe-like with a raised spire.
Keys for Patera can be found in Burch (1962), Dourson (2010 and 2015), Oesch et al. (2013), and descriptions in Hotopp et al. 2013 (see References for links). The keys that follow are a combination for the species likely to be in Indiana, so it may well be the worse of all worlds. In some cases, magnification is needed to discern shell sculpture.
Again, the key given here it is very speculative combining information from the sources given above. As with many groups, there may be more species in the state or fewer. There may be regional differences in characters as well as some characters are described differently in different sources or, at least, direct comparisons are not possible. Absent more thorough new collections and examination of museum specimens, who knows?
Key Version A
1a. Shell more globose - no apertural teeth - Patera pennsylvanica
1b. Shell more subglobose to depressed, parietal tooth present - go to 2
2a. Spiral sculpture of minute papillae – Patera appressa
2b. Spiral sculpture of spiral lines (striae) – go to 3
3a. Spiral structure of thin spiral lines, sometimes faintly visible; long low basal tooth may be poorly defined – Patera laevior
3b. Spiral structure of incised spiral lines and close transverse striae; basal tooth is blade-like and distally truncate; larger shell – Patera perigrapta (only two county occurrences)
Key Version B
1a. Shell more globose - no apertural teeth - Patera pennsylvanica
1b. Shell more subglobose to depressed, parietal tooth present - go to 2
2a. Shell more depressed with a distinctly angular body whorl perhaps more at the front than the back, long parietal tooth, long low basal tooth may be poorly defined, moderately to well-developed spiral papillae, sculpture is less coarse – Patera appressa
2b. Shell otherwise – go to 3
3b. Shell periphery less angular, more rounded; long parietal tooth, long low basal tooth which may be poorly defined; thin spiral lines on the upper surface and the base but sometimes faintly visible – Patera laevior
3c. Aperture more or less triangular, elongate; parietal lamella short and high, widely separated from the umbilical callus; incised spiral lines and close transverse striae; basal lip with a thickened ridge, terminating before the upward curve of the lip – Patera perigrapta (only two county occurrences)
See image of the Flat Bladetooth Snail
Patera appressa (Say, 1821)
Common name: Flat Bladetooth Snail
Characters: Heliciform, reflected lip, subglobose to depressed, imperforate, spiral sculpture of minute papillae, 13-21 mm.
Comparison: Patera laevior and P. perigrapta have spiral sculpture of radial lines. Xolotrema usually has a well-defined palatal tooth and basal tooth. The shell of Patera appressa is more angular at the periphery and flatter.
Habitat: can be found in rocky areas of hardwood forests and on river bluffs, but also may be associated with roads and other urban habitats.
Status: The most commonly identified Bladetooth snail, found in scattered counties in the southern half of the state.
Patera laevior (Pilsbry, 1940)
Common name: Smooth Bladetooth Snail
Characters: Heliciform, reflected lip, subglobose to depressed, imperforate, with spiral sculpture of spiral lines (striae).
Comparison: The spiral structure of Patera laevior with thin spiral lines and the basal tooth is long and low but weak; 16-23 mm.
Habitat: This species may be found in rocky areas of both natural and human habitats.
Status: Patera laevior has been collected in a few southeastern counties.
close-up of shell structure; thin spiral lines on the upper surface
Patera pennsylvanica (Green, 1827)
Common name: Proud Globelet Snail
Characters: Heliciform, reflected lip, subglobose to depressed, imperforate, 15-20 mm. This species, while a Patera, looks more like a globe snail (Mesodon).
Comparison: It can be confused with some species of Mesodon. Nearly round in apertural view, only slightly depressed. The right side of aperture is angular, not as rounded as in other Patera species. It has no teeth. Transverse striae are well-developed and spiral striae is always present and a strong feature.
Habitat: can be found under leaf litter or rocks on wooded hillsides or ravines, as well as road cuts and along abandoned railroad beds.
Status: The most commonly identified Patera, widespread in the state.
More images of the Proud Globelet Snail.
Patera perigrapta (Pilsbry, 1894)
Patera perigrapta (Pilsbry, 1894)
Common name: Engraved Bladetooth Snail
Characters: Heliciform, reflected lip, subglobose to depressed, imperforate, with spiral sculpture of spiral lines (striae).
Comparison: The spiral structure of Patera perigrapta with incised spiral lines with transverse striae and the basal tooth is narrow, like a blade, and ends sharply. See images below.
Habitat: This species may be found in rocky areas of both natural and human habitats.
Status: Patera perigrapta has been found only in two disparate counties, but is not listed in Indiana or surrounding states by Nature Serve. The records do not have a collector name or date of collection. Dourson (2010) did not recognize it in Kentucky. This is probably a spurious identification and the species is presumably not in the State.
