Valvata oregonensis is a fossil species

Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 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....

 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...

, an 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 mollusk in the family Valvatidae

Valvatidae

Valvatidae, the valve snails, is a taxonomic family of very small freshwater snails with an operculum, aquatic gastropod mollusks.- Taxonomy :...

, the valve snails.

Taylor (1966) stated, that Valvata oregonensis should be a synonym for Valvata whitei. Despite that the name Valvata oregonensis is still used (for example Pierce 1993).

Distribution

The type locality is Warner Lake beds, eastern Oregon

Eastern Oregon

Eastern Oregon is the eastern part of the U.S. state of Oregon. It is not an officially recognized geographic entity, thus the boundaries of the region vary according to context. It is sometimes understood to include only the eight easternmost counties in the state; in other contexts, it includes...

. Pliocene

Pliocene

The Pliocene Epoch is the period in the geologic timescale that extends from 5.332 million to 2.588 million years before present. It is the second and youngest epoch of the Neogene Period in the Cenozoic Era. The Pliocene follows the Miocene Epoch and is followed by the Pleistocene Epoch...

.

Valvata oregonensis was a very common species in eastern Oregon in Pleistocene

Pleistocene

The Pleistocene is the epoch from 2,588,000 to 11,700 years BP that spans the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and ....

 time. The University of Oregon

University of Oregon

-Colleges and schools:The University of Oregon is organized into eight schools and colleges—six professional schools and colleges, an Arts and Sciences College and an Honors College.- School of Architecture and Allied Arts :...

 collection contains
specimens from numerous localities about Warner Lake, Snake River Valley and in Lake County

Lake County, Oregon

Lake County is a county in the high desert south central region of the U.S. state of Oregon, so named for the many lakes found within its boundaries, including Lake Abert, Hart Lake Reservoir, and Goose Lake. While Lake is among Oregon's largest counties, it is sparsely populated with 7,895...

.

Description

The shell

Gastropod shell

The gastropod shell is a shell which is part of the body of a gastropod or snail, one kind of mollusc. The gastropod shell is an external skeleton or exoskeleton, which serves not only for muscle attachment, but also for protection from predators and from mechanical damage...

 is composed of four whorls

Whorl (mollusc)

A whorl is a single, complete 360° revolution or turn in the spiral growth of a mollusc shell. A spiral configuration of the shell is found in of numerous gastropods, but it is also found in shelled cephalopods including Nautilus, Spirula and the large extinct subclass of cephalopods known as the...

, marked with none to three spiral carinae. The spire

Spire (mollusc)

A spire is a descriptive term for part of the coiled shell of mollusks. The word is a convenient aid in describing shells, but it does not refer to a very precise part of shell anatomy: the spire consists of all of the whorls except for the body whorl...

 is normally low and umbilicus is wide, exposing all the whorls to the apex

Apex (mollusc)

Apex is an anatomical term for the tip of the mollusc shell of a gastropod, scaphopod, or cephalopod mollusc.-Gastropods:The word "apex" is most often used to mean the tip of the spire of the shell of a gastropod...

. There is great variation in the height of the spire and with its increase there is a proportionate decrease in the width of the umbilicus. The apical two whorls are flat and planulate, smooth and shining, unmarked with carinae even when the remainder of the shell may have three. Sculpture

Sculpture (mollusc)

The sculpture of a mollusc shell is the three-dimensional ornamentation on the outer surface, as distinct from the basic shape of the shell itself or colouration. Sculpture may be concave as well as convex. Sometimes it has microscopic detail. Sculpture refers to the calcareous outer layer, not the...

is comparatively uniform in character, being composed of fine growth lines.

This species is characterized by its flat nuclear whorls and generally flat shell. Only rarely is the spire as elevated, while great numbers are as flat as the lowest. The thickness of the shells is greater than in any other Valvata species.

Dimensions of the holotype and paratypes are as follows: The width of the shell is 4.6-8.0 mm. The height of the shell is 2.6-5.4 mm. In general the width of shell can reach up to 10 mm and so this is the largest species of North American Valvata.