Snails of Crystal

In many parts of the world, searching under pots or among other garden rubbish may turn up minute snails with translucent shells. Among the various families which might be found in this way are representatives of the family Pristilomatidae, commonly known as crystal snails.

Common crystal snail Vitrea crystallina, copyright O. Gargominy.

All members of the Pristilomatidae* are tiny: the minute gem snail Hawaiia minuscula, one species which has become widespread, is a giant within the family at close to three millimetres in diameter. The shells have a low spire, growing in more or less a disc shape, and are generally smooth or ornamented with very fine radial lines. In life, they are transparent or a cloudy white, explaining their vernacular name. Internal organs are often visible through the shell. The Pristilomatidae are part of the broader group of mostly tiny snails known as the Gastrodontoidea (which I've covered on this site earlier, albeit in a rather inept fashion). Even among this array, however, they are notably small. Within the gastrodontoids, the pristilomatids are primarily distinguished by the structure of the male genitalia, in which the vas deferens in attached to the proximal end of the penial tunica (a sheath of muscle tissue around the penis; Hausdorf 1998). However, there is a bit of an open question about how well supported they are as a group. Their distinguishing features could all be side effects of their reduced size.

*In older texts, you may find this family referred to as the Vitreidae, after one of the larger genera included. However, the name Pristilomatidae has priority.

Minute gem snail Hawaiia minuscula, copyright Chris Mallory.

Within their native range, crystal snails may mostly be found in western North America and the western Palaearctic. Several species, however, have become further distributed in association with humans. As such, they are mostly found in damp, disturbed habitats, such as gardens, nurseries and parks. They will be found in secluded locations such as under flower pots or buried among moss or leaf litter. Some species prefer to fully bury themselves within the soil. Some other members of the gastrodontoids are known to be predatory, feeding on small arthropods or other snails and their eggs, but I haven't been able to find any direct reference to such habits among pristilomatids. It seems more likely that they prefer to feed on decaying fragments of vegetation. They do not seem to be regarded as presenting a challenge to the gardener; rather, they may provide their own small amount of assistance in keeping things tidy.

REFERENCES

Hausdorf, B. 1998. Phylogeny of the Limacoidea sensu lato (Gastropoda: Stylommatophora). Journal of Molluscan Studies 64 (1): 35-66.

Hausdorf, B. 2000. Biogeography of the Limacoidea sensu lato (Gastropoda: Stylommatophora): vicariance events and long-distance dispersal. Journal of Biogeography 27: 379–390.