''Potamolithus rushii'' is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

freshwater snail Freshwater snails are gastropod mollusks which live in fresh water. There are many different families. They are found throughout the world in various habitats, ranging from ephemeral pools to the largest lakes, and from small seeps and springs ...

with an operculum, an aquatic

gastropod The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. T ...

mollusk Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is e ...

in the

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Lithoglyphidae Lithoglyphidae is a family of small freshwater snails with gills and an operculum, aquatic gastropod mollusks. This family is in the superfamily Truncatelloidea and in the clade Littorinimorpha (according to the taxonomy of the Gastropoda by ...

. ''Potamolithus rushii'' is the

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen ...

of the genus ''Potamolithus''. The

specific name Specific name may refer to: * in Database management systems, a system-assigned name that is unique within a particular database In taxonomy, either of these two meanings, each with its own set of rules: * Specific name (botany), the two-part (bino ...

''rushii'' is in honor of Dr. William H. Rush (18??-1918), who collected this species.

Distribution

The distribution of ''Potamolithus rushii'' includes the

Uruguay River The Uruguay River ( es, Río Uruguay, ; pt, Rio Uruguai, ) is a major river in South America. It flows from north to south and forms parts of the boundaries of Brazil, Argentina, and Uruguay, separating some of the Argentine provinces of La M ...

near

Paysandú Paysandú () is the capital of Paysandú Department in western Uruguay. Location The city is located on the banks of the Uruguay River, which forms the border with Argentina. It lies northwest of Montevideo via Route 1 and Route 3, on the ju ...

(the type locality),Pilsbry H. A. (1911). "Non-marine Mollusca of Patagonia". In: Scott W. B. (ed.) ''Reports of the Princeton University Expedition to Patagonia 1896–1899'' 3
513
633. ''Potamolithus rushii'' is on page
599
600
plate 38

Uruguay Uruguay (; ), officially the Oriental Republic of Uruguay ( es, República Oriental del Uruguay), is a country in South America. It shares borders with Argentina to its west and southwest and Brazil to its north and northeast; while bordering ...

and

Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...

.Rumi A., Gregoric D. E. G., Núñez V. & Darrigran G. A. (2008). "Malacología Latinoamericana. Moluscos de agua dulce de Argentina". '' Revista de Biología Tropical'' 56(1): 77-111
HTM

Description

''Potamolithus rushii'' was originally described by the American

malacologist Malacology is the branch of invertebrate zoology that deals with the study of the Mollusca (mollusks or molluscs), the second-largest phylum of animals in terms of described species after the arthropods. Mollusks include snails and slugs, clams, ...

Henry Augustus Pilsbry Henry Augustus Pilsbry (7 December 1862 – 26 October 1957) was an American biologist, malacologist and carcinologist, among other areas of study. He was a dominant presence in many fields of invertebrate taxonomy for the better part of a centu ...

in 1896. Pilsbry's original text reads as follows: The shell of ''Potamolithus rushii'' is imperforate, wider than high, biconvex, very solid and strong. It is light green in color. The last half of the

last whorl The body whorl is part of the morphology of the shell in those gastropod mollusks that possess a coiled shell. The term is also sometimes used in a similar way to describe the shell of a cephalopod mollusk. In gastropods In gastropods, the b ...

is dusky green. The keels are rather bright green. The early whorls are being dark reddish brown. The surface is somewhat glossy, with faint, fine growth-lines and barely perceptible spiral lines. The

spire A spire is a tall, slender, pointed structure on top of a roof of a building or tower, especially at the summit of church steeples. A spire may have a square, circular, or polygonal plan, with a roughly conical or pyramidal shape. Spires are ...

is convex, the

apex The apex is the highest point of something. The word may also refer to: Arts and media Fictional entities * Apex (comics), a teenaged super villainess in the Marvel Universe * Ape-X, a super-intelligent ape in the Squadron Supreme universe *Apex ...

is obtuse. The shell has 4

whorls A whorl ( or ) is an individual circle, oval, volution or equivalent in a whorled pattern, which consists of a spiral or multiple concentric objects (including circles, ovals and arcs). Whorls in nature File:Photograph and axial plane floral d ...

, but the first whorl is eroded, leaving a pit, in all the adult shells seen. The whorls are convex, with seam-like sutures. In the latter part of the penultimate whorl the peripheral keel is usually visible at the suture. The last whorl has a very strong peripheral keel, the surface is being concave above and below it. Above the concavity the upper surface is convex, the convexity rising into a hump on the back, then disappearing, the last fourth of the whorl being flat. The base has a thick and prominent keel, defining a concave yellowish columellar area. The outer lip has a high, narrow varix at the edge. The

aperture In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture and focal length of an optical system determine the cone angle of a bundle of rays that come to a focus in the image plane. An opt ...

is very oblique, short-ovate, nearly circular, with a continuous, black-edged margin. The oblique

columella Lucius Junius Moderatus Columella (; Arabic: , 4 – ) was a prominent writer on agriculture in the Roman Empire. His ' in twelve volumes has been completely preserved and forms an important source on Roman agriculture, together with the wo ...

is very broad, with a gutter or concavity near to and parallel with the inner margin. There is some variation in the degree of depression of the whole shell, the amplitude of the columellar area and in the prominence of the hump on the back, which is sometimes almost suppressed. The width of the shell is 6.3 mm. The height of the shell is 4.3-5.1 mm. The relationship between ''Potamolithus rushii'' and '' Potamolithus iheringi'' is exceedingly interesting. The two species are similar in general color-scheme, in the varix, absence of more rapid descent of the suture towards the mouth, etc., but are totally diverse in contour, the one being carinate, the other smooth and naticoid. Yet it is significant that while ''Potamolithus iheringi'' has no trace of a peripheral keel, the green band occupies the same position as that coloring the keel in ''Potamolithus rushii''.

Life cycle

The youngest specimens seen by Pilsbry had three whorls and a diameter of 3 mm. They had the depressed contour of adults and were strongly carinate peripherally, but the carina is distinctly weaker in front of the mouth, apparently indicating that it begins when the shell has nearly two whorls and a diameter of about a millimeter. At the 3 mm stage, the columella is very broad, semicircular, with a deep excavation and rod-like inner border (see image on the right). Very late in the neanic stage the basal keel appears, the shell then being about 5 mm in diameter; the columellar area is very narrow, at first linear. The rib or convexity of the upper surface is also of late appearance, these structures belong to the third neanic substage, the second, or unicarinate, substage thus occupying the greater part of the neanic stage. The discontinuation of the upper ridge or hump initiates the ephebic substage. The marginal varix and the absence of any tendency of the last whorl to descend or loosen its coil anteriorly, show that this species is at its acme. It has none of the stigmata of senility which are so manifest in '' Potamolithus microthauma'', '' Potamolithus hidalgoi'', etc.

References

This article incorporates public domain text from references {{Taxonbar, from=Q16988441 Lithoglyphidae Gastropods described in 1896