Pennsylvania Land Snails

Photo(s): Larry Watrous

Carychium exile I. Lea, 1842

Common name: Ice thorn
Family Carychiidae
Order Basommatophora

The ice thorn is a tiny animal that lives on the surfaces of rotting leaves in damp leaf litter. It has an elongated, delicate, whitish and translucent shell approximately 1.75mm long. A single lamella spirals around the internal spire and appears at the aperture as a single small tooth.

Most of the Keystone State's land snails are Stylommatophorans, having eyes at the tips of their upper tentacles, but the ice thorn is a Basommatophoran (as are many freshwater snails), with eyespots at the base of its tentacles, and with a different arrangement of kidney and lungs as well.

The ice thorn is widespread in the Eastern United States, including Pennsylvania, but somewhat patchy in distribution, perhaps due to its preference for richer sites. Across its range this animal is found in a wide variety of habitats including in the Great Lakes Region (Nekola, 1999) and it was found at cave entrances in the Midwest and southeast (e.g. Hobbs, 1994). In Tennessee the ice thorn was found to be positively correlated with soil moisture and soil pH (Coney et al., 1982).

The ice thorn is distinguished from its close relative, the obese thorn (Carychium exiguum), by its narrower shell, stronger sculpture of close striations, and differences in the internal lamella. Many authors previously called large examples of Carychium exile as Carychium exile canadensis, but this subspecies distinction was found to be invalid in the Great Lakes region by Nekola and Barthel (2002).

Ken Hotopp, 1/2/06

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