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Book details
  • Genre:SCIENCE
  • SubGenre:Life Sciences / Zoology / Invertebrates
  • Language:English
  • Series title:The Freshwater Gastropods of North America
  • Series Number:1
  • Pages:212
  • Paperback ISBN:9780960084302

Atlantic Drainages, Georgia Through Pennsylvania

by Robert T. Dillon, Jr. , Matthew Ashton, Will Reeves, Thomas Smith, Timothy Stewart and Brian Watson View author's profile page

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In this volume we report the results of the largest-scale inventory of freshwater snails ever conducted in the United States. We have reviewed and synthesized macrobenthic collections taken by ten natural resource agencies, malacological holdings at eight museums, and our own original collections from hundreds of sites, covering all freshwater gastropod habitat in Atlantic drainage systems from Georgia to the New York state line. Information theoretical analysis of the 12,211 record database resulting from this survey suggests that our list of 69 species is complete, with no evidence of rare species missed. For each species we provide:

  • A dichotomous key for identification.
  • Full-color figures.
  • Range maps at county scale.
  • Notes on habitat, ecology, life history, and reproductive biology.
  • Systematic and taxonomic updates to modern standards.

The distribution of commonness and rarity for this diverse and far-flung fauna did not appear lognormal, but rather bimodal, with a primary peak in the range of 16 – 64 incidences and a secondary peak in the range of 256 – 1,024. We propose a nonparametric system ranking our 69 species into five incidence categories, setting aside the rarest 5% and dividing the remainder into quartiles. Within this system we recognize subsets of peripheral (pseudo-rare) species and species demonstrating non-apparent rarity, following the work of K. J. Gaston. A new species of pleurocerid snail, Pleurocera shenandoa Dillon, is described in the appendix.


The Freshwater Gastropods of North America Project was born in the summer of 1998 at the World Congress of Malacology in Washington, DC.  It has developed into a long-term, collaborative effort to survey the entire freshwater gastropod fauna of the continental United States and Canada.  Our products were entirely web-based during our first years, with South Carolina coming online in 2003, North Carolina 2005, Georgia 2006, Virginia and East Tennessee 2011, and the Mid-Atlantic States 2013.  In the present volume we collect five previously-independent regional inventories, compile regional distribution maps, and synthesize the combined results together with ecological and systematic notes on the entire freshwater gastropod fauna of the US Atlantic drainages.

About the author
Dr. Robert T. Dillon, Jr. is America's foremost authority on freshwater gastropods. From 1983 until his retirement in 2016 he was Professor of Biology at the College of Charleston in South Carolina. He is the author of The Ecology of Freshwater Molluscs (Cambridge University Press, 2000) and over 60 scientific papers on the genetics, evolution, and ecology of snails. A former president of the American Malacological Society, Dr. Dillon wrote the freshwater gastropod chapter for the popular 2006 AMS publication, The Mollusks: A Guide to their Study, Collection and Preservation. In 1998 he founded the Freshwater Gastropods of North America Project, a long-term, collaborative effort to inventory and monograph the entire gastropod fauna inhabiting every river, lake and stream throughout the continent north of Mexico.