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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:3
  • Pages:270
  • Paperback ISBN:9780960084326

Essays On the Prosobranchs

by Robert T. Dillon, Jr.

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The rivers, lakes, and streams of North America are inhabited by a diverse assortment of gill-bearing freshwater snail populations collectively called "prosobranchs." Prosobranchs are typically longer-living and slower-growing than the more familiar pulmonate snails, inhabiting more permanent and stable bodies of water. There is reason to think that some prosobranch populations from Southern Appalachian drainages may have evolved hundreds of millions of years ago and remained morphologically unchanged ever since.

Collected in this third volume of the FWGNA Series are 37 essays on the systematics and evolutionary biology of North American prosobranch gastropods, originally published in blog form 2006 - 2019, edited and reorganized thematically. The tension between gene trees and species trees, explored at some length using pulmonate models in Volume 2, is aggravated in prosobranch populations by a phenomenon here described as "mitochondrial superheterogeneity." The challenge introduced by ecophenotypic variation in shell morphology, also evident in populations of pulmonate snails, is further explored. A new term, "Goodrichian Taxon Shift," is coined to describe intrapopulation variance so extreme as to prompt an erroneous hypothesis of speciation and generalized to "Cryptic Phenotypic Plasticity" in later chapters.

Some North American populations of freshwater prosobranch snails have been listed as objects of conservation concern. This introduces a new subtheme into Volume 3, the relationship between science and public policy. The taxonomic revisions prompted by improvements in our understanding of the evolution of prosobranchs have sometimes met resistance both from natural resource agencies and from conservation biologists dependent upon such agencies for funding. The overarching theme of the present volume becomes, then, one of a struggle to understand the evolution of the freshwater prosobranch gastropod fauna of North America, both finely scientific and clumsily human.


The Freshwater Gastropods of North America Project is a long-term, collaborative effort to survey the entire gastropod fauna inhabiting every river, lake, pond and stream in the continental United States and Canada.  Born in the summer of 1998 at the World Congress of Malacology in Washington, the effort has covered all or part of 17 eastern states to date, extending from New York to Mississippi.  In Volume 1 of this series we reported the scientific results from our survey of US Atlantic drainages from Georgia through Pennsylvania, and in Volume 2 we added 29 essays with supplementary information on the biology of the Pulmonate snails found in this vast region.

The essays published here in Volume 3 are offered as supplementary information on the evolutionary biology of the pleurocerid gastropods (Essays 1 – 27) and the hydrobioids (Essays 28 – 37).  They provide essential insight into the historical background, context, and rationale for the many methodological and taxonomic approaches advanced in Volume 1, and in Volume 5, covering the Ohio, Cumberland, and Tennessee drainages, published in 2023.

About the author

Dr. Robert T. Dillon, Jr. is America's foremost authority on freshwater gastropods. From 1983 until 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 contributed the freshwater gastropod chapter to 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, authoring or coauthoring an extensive website, a popular blog, and seven hardcopy volumes to date.