FWGNA > Species Accounts > Hydrobiidae > Marstonia scalariformis
Marstonia scalariformis (Wolf 1869)

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> Habitat & Distribution

This is another entry in the long list of small, obscure and poorly-known hydrobioid snails of North America.  The range of Marstonia scalariformis seems strikingly disjunct, with a Midwestern focus and a Southern focus.  In the former are populations inhabiting the Illinois, the Rock, and the Meramec Rivers of Illinois and Missouri, all draining into the Mississippi, with the lower Wabash River and Northern Indiana's Lake Maxinkuckee draining into The Ohio. In the southern focus are populations inhabiting the Flint River and Shoal Creek, draining into the Tennessee River of North Alabama. The single record in our Ohio database comes from the Field Museum of Natural History, a collection made by J. Gerber from the lower Wabash River in 2010.  FWGNA incidence rank I-1.

> Ecology & Life History

Little is known about the biology of any of these obscure species of Marstonia.  Berry (1943) reported that the (outwardly similar) Marstonia letsoni inhabits the "honeycombed cavities" of rocks sampled from deeper waters, which would jive with the reported absence of body pigmentation in M. scalariformis.  Such cryptic habitats seem to suggest a diet that does not ordinarily include algae, but rather very fine organic matter or bacteria, as well as (perhaps) a preference for relatively constant environmental conditions.

> Taxonomy & Systematics

Wolf (1869) described "Pyrgula" scalariformis from a single empty shell collected along the Illinois River.  Specimens have rarely been collected since.  The species was reviewed (as Pyrgulopsis scalariformis) in the excellent monograph of Hershler (1994), and transferred to the resurrected genus Marstonia by Thompson & Hershler (2002).  Marstonia was subsequently retained in the Hydrobiidae (ss) by Wilke and colleagues (2013).

In gross morphology and overall biology, Marstonia scalariformis also seems rather similar to the equally obscure M. letsoni (Walker 1901), and to the extinct Marstonia ozarkensis (Hinkley 1915). See my essay of 16Mar20 from the link below.  More research into this entire enigmatic group would be much welcomed.

> Essays

  • I explored the possibility that Marstonia ozarkensis, declared extinct by the USFWS in 2018, might have been a junior synonym of M. letsoni in my 2020 series:  What was Marstonia ozarkensis? and Is Marstonia ozarkensis extinct?  The latter essay also broached the possiblity that both letsoni (Walker 1901) and ozarkensis (Hinkley 1915) might prove junior synonyms of Marstonia scalariformis (Wolf 1869).
  • Earlier versions of this website, online until August of 2016, adopted the large, broadly-inclusive concept of the Hydrobiidae (sl) following Kabat & Hershler (1993).  More recently the FWGNA project has shifted to the Wilke et al. (2013) classification system, distinguishing a much smaller Hydrobiidae (ss) and elevating many hydrobioid taxa previously ranked as subfamilies to the full family level.  For more details, see The Classification of the Hydrobioids.

> References

Berry, E. G. (1943)  The Amnicolidae of Michigan: Distribution, ecology, and taxonomy.  Misc. Publ. Mus. Zool. Univ. Mich. 57: 1 - 68.
Hershler, R. (1994)  
A review of the North American freshwater snail genus Pyrgulopsis (Hydrobiidae).  Smithsonian Contributions to Zoology 554: 1 - 115.
Thompson, F. G. & R. Hershler (2002)  Two genera of North American freshwater snails: Marstonia Baker, 1926, resurrected to generic status, and Floridobia, new genus (Prosobranchia: Hydrobiidae: Nymphophilinae).  The Veliger 45: 269 - 271.
Wilke T., Haase M., Hershler R., Liu H-P., Misof B., Ponder W. (2013)  Pushing short DNA fragments to the limit: Phylogenetic relationships of “hydrobioid” gastropods (Caenogastropoda: Rissooidea).  Molec. Phyl. Evol. 66: 715 – 736.
Walker, B.  (1918)  A synopsis of the classification of the fresh-water mollusca of North America, North of Mexico.  University of Michigan Museum of Zoology Misc. Publ. 6: 1 - 213.
Wolf, J. (1869)  Descriptions of three new species of shells.  American Journal of Conchology 5: 198.