The Poweshiek Skipper Project

Terrestrial Snails
 

 Mesodon thyroidus (Say, 1816)

White-lipped Globe
This is also known as Helix thyroidus, Helix thyroides, and Polygyra thyroides.  

This species is found throughout the eastern United States.  It has been reported mostly from the eastern counties of Iowa that border the Mississippi, although it is probably widespread in forested areas of Iowa.

I found this species at Maquoketa Caves State Park in Jackson County, Iowa.  A number of smaller individuals were found on the upper surfaces of stinging nettles and a large individual was found on the woodland floor.

The species has an open umbilicus that is partly covered by the reflected lip.  Most individuals have a denticle on the parietal (inner) wall according to some of the guide books, but this is impossible to verify on the living animals.

I was surprised by the length that the snail was able to extend the upper tentacles containing the eye stalks.  The eye stalks can be extended to unusually long lengths in this species, both in the smaller and the larger individuals.

 

Baker makes the observation that these snails are often found in "colonies" that contain individuals in a wide variety of sizes.  That was certainly the case when I found these.  I was also surprised to find a number of them exposed, on the upper surfaces of  plants.  Perhaps the stinging nettles that they were on provided a degree of protection.