Plicate rocksnail
Encyclopedia
The plicate rocksnail, scientific name Leptoxis plicata, is a species
of freshwater snail
with a gill and an operculum
, an aquatic
gastropod mollusk in the family Pleuroceridae
.
This species is endemic to the United States
, specifically the state of Alabama
. The snail has been listed as endangered on the United States Fish and Wildlife Service list of endangered species
since October 28 1998.
that grows to about 20 mm (0.8 in) in length. Shells are subglobose with broadly rounded apertures
. The body whorl
may be ornamented with strong folds or plicae. Shell color is usually brown, occasionally green, and often with four equidistant color bands. The columella (central column or axis) is smooth, rounded, and typically pigmented in the upper half. The aperture is usually bluish-white, occasionally pink or white.
The operculum
(plate that closes the shell when the snail is retracted) is dark red, and moderately thick.
Although morphologically similar to the Basin's other three surviving rocksnail species, the plicate rocksnail is genetically distinct
.
, the Little Warrior River
, and the Tombigbee River
.
Recent status surveys have located plicate rocksnail populations only in an approximately 88 km (55 mi) reach of the Locust Fork of the Black Warrior River
, Jefferson
and Blount counties, Alabama
. The latest survey information indicates that the snail has recently disappeared from the upstream two-thirds portion of that habitat and now appears to be restricted to an approximately 32 km (20 mi) reach in Jefferson County.
Basin's larger rivers - (Black Warrior River, the Little Warrior River, and the Tombigbee River for the Plicate rocksnail) is primarily due to extensive construction of dam
s, and the subsequent inundation of the snail's shoal habitats by the impounded waters. This snail has disappeared from all portions of its historic habitats that have been impounded by dams.
Dams change such areas by eliminating or reducing currents, and thus allowing sediments to accumulate on inundated channel habitats. Impounded waters also experience changes in water chemistry, which could affect survival or reproduction of riverine snails. For example, many reservoirs in the Basin currently experience eutrophic (enrichment of a water body with nutrients) conditions, and chronically low dissolved oxygen levels. Such physical and chemical changes can affect feeding, respiration, and reproduction of these riffle and shoal snail 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
Snail
Snail is a common name applied to most of the members of the molluscan class Gastropoda that have coiled shells in the adult stage. When the word is used in its most general sense, it includes sea snails, land snails and freshwater snails. The word snail without any qualifier is however more often...
with a gill 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 Pleuroceridae
Pleuroceridae
Pleuroceridae, common name pleurocerids, is a family of small to medium-sized freshwater snails, aquatic gilled gastropod mollusks in the superfamily Cerithioidea.These snails have an operculum and typically a robust high-spired shell....
.
This species is endemic to the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, specifically the state of Alabama
Alabama
Alabama is a state located in the southeastern region of the United States. It is bordered by Tennessee to the north, Georgia to the east, Florida and the Gulf of Mexico to the south, and Mississippi to the west. Alabama ranks 30th in total land area and ranks second in the size of its inland...
. The snail has been listed as endangered on the United States Fish and Wildlife Service list of endangered species
United States Fish and Wildlife Service list of endangered species
This list contains only the bird and mammal species described as endangered by the United States Fish and Wildlife Service. It contains species not only in the U.S. and its territories, but also species only found abroad. It does not contain fish, amphibians, reptiles, plants, or invertebrates,...
since October 28 1998.
Description
The plicate rocksnail is a pleurocerid snail with a shellGastropod 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...
that grows to about 20 mm (0.8 in) in length. Shells are subglobose with broadly rounded apertures
Aperture (mollusc)
The aperture is an opening in certain kinds of mollusc shells: it is the main opening of the shell, where part of the body of the animal emerges for locomotion, feeding, etc....
. The body whorl
Body whorl
Body whorl is part of the morphology of a coiled gastropod mollusk.- In gastropods :In gastropods, the body whorl, or last whorl, is the most recently-formed and largest whorl of a spiral or helical shell, terminating in the aperture...
may be ornamented with strong folds or plicae. Shell color is usually brown, occasionally green, and often with four equidistant color bands. The columella (central column or axis) is smooth, rounded, and typically pigmented in the upper half. The aperture is usually bluish-white, occasionally pink or white.
The 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...
(plate that closes the shell when the snail is retracted) is dark red, and moderately thick.
Although morphologically similar to the Basin's other three surviving rocksnail species, the plicate rocksnail is genetically distinct
Population genetics
Population genetics is the study of allele frequency distribution and change under the influence of the four main evolutionary processes: natural selection, genetic drift, mutation and gene flow. It also takes into account the factors of recombination, population subdivision and population...
.
Distribution
The plicate rocksnail historically occurred in the Black Warrior RiverBlack Warrior River
The Black Warrior River is a waterway in west central Alabama in the southeastern United States. The river rises in the extreme southern edges of the Appalachian Highlands and flows 178 miles to the Tombigbee River, of which the Black Warrior is the primary tributary...
, the Little Warrior River
Little Warrior River
Little Warrior River is a river in Blount County, Alabama. It is a tributary of the Locust Fork of the Black Warrior River. The Little Warrior River forms near the town of Locust Fork at the confluence of the Blackburn Fork and Calvert Prong....
, and the Tombigbee River
Tombigbee River
The Tombigbee River is a tributary of the Mobile River, approximately 200 mi long, in the U.S. states of Mississippi and Alabama. It is one of two major rivers, along with the Alabama River, that unite to form the short Mobile River before it empties into Mobile Bay on the Gulf of Mexico...
.
Recent status surveys have located plicate rocksnail populations only in an approximately 88 km (55 mi) reach of the Locust Fork of the Black Warrior River
Locust Fork of the Black Warrior River
The Locust Fork, in Blount, Etowah, and Marshall counties is one of three major tributaries of the Black Warrior River. The river features several stretches of whitewater, and is popular with canoers and kayakers. In the late 1980s, the Birmingham Water Works proposed damming the river as a...
, Jefferson
Jefferson County, Alabama
Jefferson County is the most populous county in the U.S. state of Alabama, with its county seat being located in Birmingham.As of the 2010 U.S. Census, the population of Jefferson County was 658,466...
and Blount counties, Alabama
Blount County, Alabama
Blount County is a county located in the U.S. state of Alabama. As of the 2010 United States Census, the population was 57,322. Its county seat is Oneonta.Blount County is a dry county.-History:...
. The latest survey information indicates that the snail has recently disappeared from the upstream two-thirds portion of that habitat and now appears to be restricted to an approximately 32 km (20 mi) reach in Jefferson County.
Reasons for the decline
The Plicate rocksnail has disappeared from more than 90 percent of its historic range. The curtailment of habitat and range for this species (and a few other snail species) in the MobileMobile River
The Mobile River is located in southern Alabama in the United States. Formed out of the confluence of the Tombigbee and Alabama rivers, the approximately river drains an area of of Alabama, with a watershed extending into Mississippi, Georgia, and Tennessee. Its drainage basin is the...
Basin's larger rivers - (Black Warrior River, the Little Warrior River, and the Tombigbee River for the Plicate rocksnail) is primarily due to extensive construction of dam
Dam
A dam is a barrier that impounds water or underground streams. Dams generally serve the primary purpose of retaining water, while other structures such as floodgates or levees are used to manage or prevent water flow into specific land regions. Hydropower and pumped-storage hydroelectricity are...
s, and the subsequent inundation of the snail's shoal habitats by the impounded waters. This snail has disappeared from all portions of its historic habitats that have been impounded by dams.
Dams change such areas by eliminating or reducing currents, and thus allowing sediments to accumulate on inundated channel habitats. Impounded waters also experience changes in water chemistry, which could affect survival or reproduction of riverine snails. For example, many reservoirs in the Basin currently experience eutrophic (enrichment of a water body with nutrients) conditions, and chronically low dissolved oxygen levels. Such physical and chemical changes can affect feeding, respiration, and reproduction of these riffle and shoal snail species.