Marstonia is a genus

Genus

In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 of freshwater snail

Freshwater snail

A freshwater snail is one kind of freshwater mollusc, the other kind being freshwater clams and mussels, i.e. freshwater bivalves. Specifically a freshwater snail is a gastropod that lives in a watery non-marine habitat. The majority of freshwater gastropods have a shell, with very few exceptions....

s with a gill

Gill

A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...

 and an operculum

Operculum (gastropod)

The operculum, meaning little lid, is a corneous or calcareous anatomical structure which exists in many groups of sea snails and freshwater snails, and also in a few groups of land snails...

, aquatic

Aquatic animal

An aquatic animal is an animal, either vertebrate or invertebrate, which lives in water for most or all of its life. It may breathe air or extract its oxygen from that dissolved in water through specialised organs called gills, or directly through its skin. Natural environments and the animals that...

 gastropod mollusks in the family Hydrobiidae

Hydrobiidae

Hydrobiidae, common name mud snails, is a large cosmopolitan taxonomic family of very small freshwater snails and brackish water snails that have an operculum, aquatic gastropod mollusks in the clade Littorinimorpha.- Distribution :...

.

Distribution

Species in the genus Marstonia are distributed in springs, streams and lakes in eastern North America. Most of these species have extremely narrow geographic ranges and consequently have become a focus of conservation activities; two are federally listed as endangered and others are variously listed by state wildlife agencies.

Description

The freshwater gastropod genus Marstonia is composed of 15 small (shell height < 5.0 mm), ovate- to elongate-shelled species. Marstonia differs from the other eight North American nymphophiline genera in that the (female) oviduct and bursal duct join well in front of (instead of behind) the posterior wall of the pallial cavity. It has also been resolved as a well supported sub-clade within its subfamily based on mtDNA sequences.

Species

Eastern North American species of Pyrgulopsis

Pyrgulopsis

Pyrgulopsis is a genus of freshwater snails with a gill and an operculum, aquatic gastropod mollusks in the family Hydrobiidae.- Etymology :The name Pyrgulopsis is composed from Pyrgula and opsis = aspect of.- Shell description :...

are considered to be in separate genus Marstonia according to Thompson & Hershler (2002).

• Marstonia agarhecta (F. G. Thompson, 1969) - synonym: Pyrgulopsis agarhecta F. G. Thompson, 1969 - Ocmulgee marstonia
• Marstonia arga - F. G. Thompson, 1977 - synonym: Pyrgulopsis arga (F. G. Thompson, 1977) - ghost marstonia
• Marstonia castor F. G. Thompson, 1977 - synonym: Pyrgulopsis castor (F. G. Thompson, 1977) - beaverpond marstonia
• Marstonia halcyon F. G. Thompson, 1977 - synonym: Pyrgulopsis halcyon (F. G. Thompson, 1977) - halcyon marstonia
• Marstonia hershleri (F. G. Thompson, 1995) - synonym: Pyrgulopsis hershleri F. G. Thompson, 1995 - Coosa pyrg
• Marstonia letsoni (Walker, 1901) - synonym: Pyrgulopsis letsoni (Walker, 1901) - gravel pyrg
• Marstonia lustrica (Pilsbry, 1890) - synonym: Pyrgulopsis lustrica (Pilsbry, 1890) - boreal marstonia
• Marstonia ogmorhaphe (F. G. Thompson, 1977) - synonym: Pyrgulopsis ogmoraphe (F. G. Thompson, 1977) - royal springsnail
• Marstonia olivacea (Pilsbry, 1895) - synonym: Pyrgulopsis olivacea (Pilsbry, 1895) - olive marstonia, it may be extinct
• Marstonia ozarkensis (Hinkley, 1915) - synonym: Pyrgulopsis ozarkensis Hinkley, 1915 - Ozark pyrg, it may be extinct
• Marstonia pachyta F. G. Thompson, 1977 - synonym: Pyrgulopsis pachyta (F. G. Thompson, 1977) - armored marstonia
• Marstonia scalariformis
  Marstonia scalariformis
  Marstonia scalariformis, previously known as Pyrgulopsis scalariformis, common name the moss pyrg, is a species of freshwater snail with a gill and an operculum, aquatic gastropod mollusk in the family Hydrobiidae.- Shell description :...
  
  (Wolf, 1869) - synonym: Pyrgulopsis scalariformis (Wolf, 1869) - moss pyrg

Other species of Marstonia include:

• Marstonia angulobasis F. G. Thompson, 2005 - Angled Marstonia
• Marstonia comalensis
  Marstonia comalensis
  Marstonia comalensis is a species of minute freshwater snail with a gill and an operculum, an aquatic gastropod mollusk or micromollusk in the family Hydrobiidae. It is found in south central Texas, USA....
  
  (Pilsbry & Ferriss, 1906) - Comal Siltsnail
• Marstonia gaddisorum F. G. Thompson, 2004 - Gaddis Marstonia

Although Marstonia has been reviewed four times since 1978 (Thompson 1978, Hershler 1994, Thompson & Hershler 2002, Hershler & Liu 2011), three of its congener

Congener

Congener has several different meanings depending on the field in which it is used. Colloquially, it is used to mean a person or thing like another, in character or action.-Biology:In biology, congeners are organisms within the same genus...

s have been little studied beyond their original descriptions and their anatomy is unknown. Two of these — Marstonia olivacea, Marstonia ozarkensis — may be extinct and thus will likely remain incertae sedis

Incertae sedis

, is a term used to define a taxonomic group where its broader relationships are unknown or undefined. Uncertainty at specific taxonomic levels is attributed by , , and similar terms.-Examples:*The fossil plant Paradinandra suecica could not be assigned to any...

.

Further reading

• Thompson F. G. & Hershler R. (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(3): 269-271.