Land Snails

Photo(s): A putative Mesodon clausus shell © Larry Watrous.

Click photo(s) to enlarge.

Mesodon clausus (Say, 1821)

Family: Polygyridae
Common name: Yellow Globelet

Identification
Width: 13.6 - 18.0 mm
Height: 10 - 13 mm
Whorls: 5+

This snail has a globe-shaped shell, and a slit-like umbilicus partly covered by the reflected peristome. There are no teeth in the aperture. The shell surface is finely and closely striate. The shell is very similar to that of M. thyroidus, though usually smaller and lacking a parietal tooth. Mesodon clausus may be a spurious description of M. thyroidus colonies living in calcium-poor habitats, resulting in smaller toothless shells.

Ecology
Like M. thyroidus this snail is patchy in distribution, and often along river floodplains and wetlands.

Taxonomy
Emberton (1991) found a close relationship between M. clausus and M. thyroidus but claimed a small shift in reproductive anatomy and allozymes. Synonyms for this species include Mesodon clausa, Helix clausa, H. ingallsi, H. jugallsiana, Triodopsis thyroidus edentula, Polygyra clausa.

Distribution
Mesodon clausus is distributed in the southern, midwestern and eastern United States, sympatric with the range of M. thyroidus. It is reported in western Virginia counties.

Conservation
NatureServe Global Rank: G5, Secure
Virginia’s wildlife action plan: Tier IV

 

Ken Hotopp 4/2013

Range Map (click to enlarge)