Classification Controversy

      When a species is first classified it is reviewed by specialists and often times will be moved several times before finding a permanent home. Currently the species Millerex lithica is under such scrutiny and in the world of snail classification, its story is proving to be very entertaining.

      In 1961, the late Dr. Hubricht, a specialist and trail blazer in the terrestrial snail world, came across a new species of snail in Northern Arkansas that he placed into the Genus Polygyra based on shell description stating that it was a variation of the P. dorfeuilliana species (Walsh, 2006). At this time Hubricht did not give specifics of the shell morphology.

      For twenty years, the species existed as Polygyra lithica until a Doctor of Philosophy student at the University of Arizona, William Lloyd Pratt Jr. wrote his dissertation, A Revision of the Land Snail Genus Polygyra in Texas. Pratt mainly focused his research on Western Texas, and while focusing on Polygyra mooreana and Polygyra derfeulliana Pratt created a new genus, Millerelix, to encompass snails with a specific shell variation and a slender penis (Pratt, 1981). While moving P. mooreana and P. derfeulliana to the Millerelix genus, Pratt used the knowledge gathered by Hubricht on P. lithica and concluded that P. lithica was precisely between P. mooreana and P. derfeulliana in the shell morphology, therefore reclassified the snail as M. lithica as it is described on this website (Pratt, 1981).

       In 1985, while researching snail specimens in Arkansas, Dr. Hubricht discovered that the M. lithica habitat was shared with M. dorfeuilliana, but maintained his stance that they were two different species, stating that the two snails held different niches in the same environment, implying no cross breeding was taking place (Walsh, 2006). This research sparked the interest of two scientists, Walsh and Coles, who in 2006 wrote, Daedalochila lithica and Daedalochila dorfeuilliana (Gastropoda: Polygyridae) in Arkansas, USA: morphology, distribution, and habitat, a paper that for the first time included work with the specific snail M. lithica. Through work with specimens, Walsh and Coles concluded that these snails did not belong in the Millerelix genus based on too much of a fluctuation of penis size and the presence of ridges in the terminal penis called papilla (Walsh, 2006). Walsh and Coles concluded that M. lithica should be moved to the genus Daedalochila based on their belief that the use of the genus Millerelix should be reassessed. In the conclusion of their paper, Walsh and Coles acknowledge that Pratt's creation of the genus Millerelix is probably valid, but feel that it has lost credit through miss-use by other scientists (Walsh, 2006).

      Upon the creation of this website, it was concluded that Millerelix lithica is the most accurate classification of the species. Although Walsh and Coles are pushing to move the species to the genus Daedalochila, they did not actually dissect a M. lithica specimen because a wet-specimen for this species was not available. Instead of going to the field to find specimens they used the results of the dissection of the relative species D. dorfeuilliana (Walsh, 2006). This insight into the world of classification illustrates the scrutiny that new classifications go under and shows the dedication of scientists to never settle for the easy answer, but instead to push for the truth.

Click here to continue reading to learn about the habitat of M. lithica

last updated November 29, 2012