FWGNA > Species Accounts > Pleuroceridae > Lithasia armigera
Lithasia armigera (Say 1821)
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> Habitat & Distribution

Goodrich (1940) focused the distribution of L. armigera in the main Cumberland River, from Burnside (KY) to mouth, including major tributaries such as the Harpeth and the Stone's. Goodrich extended the range of L. armigera into the "lower Ohio River and Lower Wabash River," plus the main Tennessee River in the vicinity of Florence, AL.  Our survey has indeed confirmed substantial populations in the lower Ohio and lower Wabash, and would add scattered records 900 miles up the Ohio River almost as far as Pittsburgh.  Tiemann et al. (2013) reported populations in the main Mississippi River.  As is true for the genus generally, populations of L. armigera  reach maximum abundance grazing on solid substrates (including gravel and cobble), which can be few and far between throughout this (rather extensive) range. FWGNA incidence rank I-4.

> Ecology & Life History

Pleurocerids are heavily-shelled, conspicuous freshwater gastropods, typically inhabiting firm substrates in shallow waters.  Males are aphallic; females can be distinguished by an egg laying groove on the right side of their foot.  Most populations are perennial and iteroparous, typically requiring more than a year to mature and living several years (Life cycle Hi of Dillon 2000: 156-162).  Eggs are affixed to hard substrates singly or in small clusters from spring to midsummer.  Pleurocerids are generalized grazers, and where present in high density can have significant effects on energy flow in streams (Dillon 2000: 86-91).

> Taxonomy & Systematics

Tryon (1873) catalogued 25 species in the genus Lithasia/Angitrema, primarily inhabiting the Tennessee/Cumberland but ranging throughout the interior drainages of seven states.  Among Calvin Goodrich's greatest contributions to science was his (1934) documentation that three of these nomina: geniculata (Haldeman), fuliginosa (Lea) and pinguis (Lea), were shell variants of a single species inhabiting the Duck River of middle Tennessee in clinal series.  This observation presaged our understanding of "cryptic phenotypic plasticity" in the North American Pleuroceridae (Dillon 2011, 2014; Dillon et al. 2013) by 80 years.  Goodrich lowered fuliginosa and pinguis to subspecific rank under geniculata, ultimately (in 1940) boiling Tryon's 25 species down to 10 species and 14 subspecies.  Burch (1989) left Goodrich's system almost untouched, trimming out one species and 8 subspecies, but adding one species more recently described, to bring the total back to 10.

Minton & Lydeard (2003) obtained mtDNA CO1 sequence data from 5 populations of L. armigera:  Ohio R (2 individuals), Wabash R (2), Tennessee R (1), Stone's R (6), and Harpeth R (3).  All 14 individuals sampled, from 5 populations, were genetically indistinguishable.  But the grouping of the entire genus Lithasia within the Pleuroceridae, based on CO1 sequences, did not agree with a grouping previously published by Holznagel and Lydeard (2000) based on 16S sequences.  This observation led Minton and his colleagues (2005) to focus on the Harpeth River population of L. armigera and ultimately, on the basis of CO1 sequence and radular wear, describe a new species, L. spicata.  See my 2016 series on mitochondrial superheterogeneity from the links below for a better explanation.

> Supplementary Resources

> Essays

> References

Burch, J. B. (1989)  North American Freshwater Snails.  Malacological Publications, Hamburg, MI.
Dillon, R. T., Jr. (1989)
  Karyotypic evolution in pleurocerid snails: I. Genomic DNA estimated by flow cytometry. Malacologia, 31: 197-203. 
Dillon, R. T., Jr. (2000)  The Ecology of Freshwater Molluscs. Cambridge, Cambridge University Press.  509 pp.

Dillon, R. T., Jr. (2011)  Robust shell phenotype is a local response to stream size in the genus Pleurocera.  Malacologia 53: 265-277.  [pdf]
Dillon, R. T., Jr.  (2014) Cryptic phenotypic plasticity in populations of the North American freshwater gastropod, Pleurocera semicarinata.  Zoological Studies 53:31. [html] [pdf]
Dillon, R. T., Jr., S. J. Jacquemin & M. Pyron (2013) Cryptic phenotypic plasticity in populations of the freshwater prosobranch snail, Pleurocera canaliculata.  Hydrobiologia 709: 117-127. [html] [pdf]
Goodrich, C. (1934) Studies of the gastropod family Pleuroceridae - I.  Occas. Pprs. Mus. Zool. Univ. Mich. 286: 1 - 17.
Goodrich, C. (1940) The Pleuroceridae of the Ohio River drainage system.  Occas. Pprs. Mus. Zool. Univ. Mich., 417: 1-21.
Goodrich, C. (1941) Studies of the gastropod family Pleuroceridae VIII.  Occas. Pprs. Mus. Zool. Univ. Mich. 447: 1 - 13.
Holznagel, W. E. & C. Lydeard (2000)  A molecular phylogeny of North American Pleuroceridae (Gastropoda: Cerithioidea) based on mitochondrial 16S rDNA sequences.  Journal of Molluscan Studies 66: 233 - 257.
Minton, R. L. (2002)  A cladistic analysis of Lithasia (Gastropoda: Pleuroceridae) using morphological characters.  The Nautilus 116: 39-49.
Minton, R. L. (2013) A new species of Lithasia (Gastropoda: Pleuroceridae) from the Buffalo River, Tennessee, USA.  The Nautilus 127: 119 - 124.
Minton, R. L., K. C. Hart, R. Fiorillo, & C. Brown (2018)  Correlates of snail shell variation along a unidirectional freshwater gradient in Lithasia geniculata (Haldeman, 1840) (Caenogastropoda: Pleuroceridae) from the Duck River, Tennessee, USA.  Folia Malacologica 26: 95 - 102.
Minton, R. L. & C. Lydeard (2003) Phylogeny, taxonomy, genetics, and global heritage ranks of an imperiled, freshwater snail genus Lithasia (Pleuroceridae)  Molecular Ecology 12: 75-87.
Minton, R. L., A. P. Norwood & D. M. Hayes (2008) Quantifying phenotypic gradients in freshwater snails: a case study in Lithasia (Gastropoda: Pleuroceridae)  Hydrobiologia 605: 173-182
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Minton, R. L., S. P. Savarese & D. C. Campbell (2005) A new species of "Lithasia" (Mollusca: Caenogastropoda: Pleuroceridae) from the Harpeth River, Tennessee, USA.  Zootaxa 1054: 31 - 42.
Tiemann, J. S., W. R. Posey, K. S. Cummings, K. J. Irwin, and B. Turner (2013)  First occurrences of Lithasia armigera and Lithasia verrucosa (Gastropoda: Pleuroceridae) in the Mississippi River.  Southeastern Naturalist 12: N35 - N39.
Tryon, G. W. (1873) Land and Fresh-water shells of North America.  Part IV, Strepomatidae.  Smithsonial Miscellaneous Collections 253: 1- 434.