The lacy elimia, also known as the lacey elimia,

scientific name In Taxonomy (biology), taxonomy, binomial nomenclature ("two-term naming system"), also called binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, both of which use Latin gramm ...

''Elimia crenatella'', is a

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

freshwater snail Freshwater snails are gastropod mollusks that 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 t ...

with a gill and an operculum, an

aquatic Aquatic means relating to water; living in or near water or taking place in water; does not include groundwater, as "aquatic" implies an environment where plants and animals live. Aquatic(s) may also refer to: * Aquatic animal, either vertebrate ...

gastropod Gastropods (), commonly known as slugs and snails, belong to a large Taxonomy (biology), taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, freshwater, and fro ...

mollusk Mollusca is a phylum of protostomic invertebrate animals, whose members are known as molluscs or mollusks (). Around 76,000 extant species of molluscs are recognized, making it the second-largest animal phylum after Arthropoda. The ...

in the family

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. Reproduc ...

. This species is

endemic Endemism is the state of a species being found only in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also foun ...

to the

United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...

, specifically the state of

Alabama Alabama ( ) is a U.S. state, state in the Southeastern United States, Southeastern and Deep South, Deep Southern regions of the United States. It borders Tennessee to the north, Georgia (U.S. state), Georgia to the east, Florida and the Gu ...

. The snail has been listed as threatened on the

United States Fish and Wildlife Service list of endangered species This is a list of the bird and mammal species and subspecies described as endangered by the United States Fish and Wildlife Service. It contains species and subspecies not only in the U.S. and its territories, but also those only found in other ...

since October 28, 1998.

Description

The lacy elimia is a small species in the family Pleuroceridae. Growing to about 1.1 centimeters (cm) (0.4 in) in length, the

shell Shell may refer to: Architecture and design * Shell (structure), a thin structure ** Concrete shell, a thin shell of concrete, usually with no interior columns or exterior buttresses Science Biology * Seashell, a hard outer layer of a marine ani ...

is conic in shape, strongly striate, and often folded in the upper

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). In nature File:Photograph and axial plane floral diagram ...

. The shell color is dark brown to black, often purple in the

aperture In optics, the aperture of an optical system (including a system consisting of a single lens) is the hole or opening that primarily limits light propagated through the system. More specifically, the entrance pupil as the front side image o ...

, and without banding. The aperture is small and ovate. The lacy elimia is easily distinguished from other ''

Elimia ''Elimia'' is a genus of freshwater snails in the family Pleuroceridae. Species of the genus are aquatic gastropod mollusks that have an operculum. Various species are found in creeks throughout much of the eastern and central United States and ...

'' species by a combination of characters (i.e., size, ornamentation, color).

Genetics

In a recent

genetic sequence Genetic may refer to: *Genetics, in biology, the science of genes, heredity, and the variation of organisms **Genetic, used as an adjective, refers to genes *** Genetic disorder, any disorder caused by a genetic mutation, whether inherited or de no ...

study of the

16S ribosomal RNA 16S ribosomal RNA (or 16 S rRNA) is the RNA component of the 30S subunit of a prokaryotic ribosome ( SSU rRNA). It binds to the Shine-Dalgarno sequence and provides most of the SSU structure. The genes coding for it are referred to as 16S ...

gene, the lacy elimia was found to be very similar to the compact elimia ('' Elimia showalteri''). Despite their apparent close genetic relationship, the authors made no suggestion that the two species represented a single species. Upon review of Lydeard et al. (1997), Dillon suggested that additional genetic studies were needed to demonstrate the genetic uniqueness of the lacy elimia. However, the Lydeard et al. (1997) genetic study addressed only one small genetic character of the

genome A genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding genes, other functional regions of the genome such as ...

(entire genetic make-up of an individual) of these species, and other characters strongly support the taxonomic status of the lacy elimia. The two species are

allopatric Allopatric speciation () – also referred to as geographic speciation, vicariant speciation, or its earlier name the dumbbell model – is a mode of speciation that occurs when biological populations become geographically isolated from ...

(do not overlap in distribution - the compact elimia occurs in the

Cahaba River The Cahaba River is the longest substantially free-flowing river in Alabama. It is a major tributary of the Alabama River and part of the larger Mobile River basin. With headwaters near Birmingham, the Cahaba flows southwest, then at Heiberger tu ...

, whereas the lacy elimia is found in the

Coosa River The Coosa River is a tributary of the Alabama River in the U.S. states of Alabama and Georgia (U.S. state), Georgia. The river is about long.U.S. Geological Survey. National Hydrography Dataset high-resolution flowline dataThe National Map, ac ...

drainage), and are strikingly different in size, appearance, and behavior. The compact elimia has a large, robust, smooth shell boldly colored brown and/or green, whereas the lacy elimia has a small, delicate, darkly colored, and ornamented shell. The lacy elimia is one of the few elimia snails in the Basin that does not exhibit

clinal variation In biology, a cline is a measurable gradient in a single characteristic (or biological trait) of a species across its geographical range. Clines usually have a genetic (e.g. allele frequency, blood type), or phenotypic (e.g. body size, skin pig ...

.Goodrich C. 1936. ''Goniobasis of the Coosa River, Alabama''. Miscellaneous Publications, Museum of Zoology, University of Michigan (31):1-60. In addition, compact elimia are found grazing individually throughout shoal habitats, whereas the lacy elimia is usually found in tight clusters or colonies on larger rocks within a shoal. Allopatry, morphology, and behavior are strong characters supporting the species status of the lacy elimia.

Distribution

Map of Alabama highlighting Talladega County

The lacy elimia was historically abundant in the

main stem from St. Clair County, Alabama to

Chilton County, Alabama Chilton County is a county located in the central portion of the U.S. state of Alabama. As of the 2020 census, the population was 45,014. The county seat is Clanton. Its name is in honor of William Parish Chilton, Sr. (1810–1871), a lawye ...

, and was also known in several Coosa River tributaries:

Big Will's Creek Big or BIG may refer to: * Big, of great size or degree Film and television * ''Big'' (film), a 1988 fantasy-comedy film starring Tom Hanks * ''Big'', a 2023 Taiwanese children's film starring Van Fan and Chie Tanaka * ''Big!'', a Discovery ...

, DeKalb County; Kelley's Creek, St. Clair County; and

Choccolocco Creek The Choccolocco Creek is one of two main tributaries of the Coosa River in central Alabama. The watershed of the creek comprises 246,000 acres (376 mi2) of drainage area. The waterway runs through the Talledega National Forest (also referre ...

and Tallaseehatchee Creek, Talladega County, Alabama. Currently, the lacy elimia is only known to survive in three Coosa River tributaries: Cheaha Creek, Emauhee Creek, and Weewoka Creek,

Talladega County, Alabama Talladega County is one of the sixty-seven counties located in the east central portion of the U.S. state of Alabama."ACES Winston County Office" (links/history), Alabama Cooperative Extension System (ACES), 2007, webpageACES-Talladega As of t ...

. The species is locally abundant in the lower reaches of Cheaha Creek. This stream originates within the

Talladega National Forest The Talladega National Forest is located in the U.S. state of Alabama and covers 392,567 acres (613.39 sq mi, or 1,588.66 km2) at the southern edge of the Appalachian Mountains. Before it was bought by the federal government in the 1930s, ...

; however, no specimens of the lacy elimia have been collected on

United States Forest Service The United States Forest Service (USFS) is an agency within the United States Department of Agriculture, U.S. Department of Agriculture. It administers the nation's 154 United States National Forest, national forests and 20 United States Natio ...

lands. The species has also been found at single sites in Emauhee and Weewoka creeks, where specimens are rare, and difficult to locate. All of these streams are variously impacted by sediments and nutrients from a variety of upstream rural, suburban, and/or urban sources. Because of their small sizes and limited flows, their water and habitat quality can be rapidly affected by local and off site pollution sources.

Reasons for the decline

The lacy elimia has disappeared from more than 90 percent of its historic range. The curtailment of habitat and range for this (and few other snail species) species in the Mobile Basin's larger rivers (Coosa River for lacy elimia) is primarily due to extensive construction of

dam A dam is a barrier that stops or restricts the flow of surface water or underground streams. Reservoirs created by dams not only suppress floods but also provide water for activities such as irrigation, human consumption, industrial use, aqua ...

s, and the subsequent

inundation A flood is an overflow of water ( or rarely other fluids) that submerges land that is usually dry. In the sense of "flowing water", the word may also be applied to the inflow of the tide. Floods are of significant concern in agriculture, civi ...

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.

Ecology

Little is known of the ecology specific to the lacy elimia, however, common information about genus ''Elimia'' are as follows.

Habitat

Elimia snails are gill-breathing snails that typically inhabit highly oxygenated waters on rock shoals and gravel bars. It is associated with river or stream habitats characterized by flowing currents, and hard, clean bottoms (e.g., bedrock, boulder, gravel).

Feeding habits

Most elimia species graze on

periphyton Periphyton is a complex mixture of algae, cyanobacteria, heterotrophic microbes, and detritus that is attached to submerged surfaces in most aquatic ecosystems. The related term Aufwuchs ( German "surface growth" or "overgrowth", ) refers to the ...

(attached algae) growing on benthic (bottom) substrates.

Life cycle

Individual snails are either male or female. Eggs are laid in early spring and hatch in about 2 weeks. Snails apparently become sexually mature in their first year, but, in some cases, females may not lay eggs until their second year. Some elimia species may live as long as 5 years.Dillon, R.T., Jr. 1988. ''Evolution from transplants between genetically distinct populations of freshwater snails''. Genetica 76: 111-119.

References

This article incorporates public domain text (a

public domain The public domain (PD) consists of all the creative work to which no Exclusive exclusive intellectual property rights apply. Those rights may have expired, been forfeited, expressly Waiver, waived, or may be inapplicable. Because no one holds ...

work of the United States Government A work of the United States government is defined by the United States copyright law of the United States, copyright law, as "a work prepared by an officer or employee of the United States Government as part of that person's official duties".: ...

) from the reference. U.S. Fish and Wildlife Service. 2005
''Recovery Plan for 6 Mobile River Basin Aquatic Snails''
U.S. Fish and Wildlife Service, Jackson, Mississippi. 46 pp. {{DEFAULTSORT:Lacy Elimia Elimia Endemic molluscs of the United States Endemic fauna of Alabama Freshwater animals of North America Gastropods described in 1860 Taxonomy articles created by Polbot Taxa named by Isaac Lea ESA threatened species