Theodoxus fluviatilis
Encyclopedia
Theodoxus fluviatilis, common name
Common name
A common name of a taxon or organism is a name in general use within a community; it is often contrasted with the scientific name for the same organism...

 the river nerite, is a small 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 and brackish water
Brackish water
Brackish water is water that has more salinity than fresh water, but not as much as seawater. It may result from mixing of seawater with fresh water, as in estuaries, or it may occur in brackish fossil aquifers. The word comes from the Middle Dutch root "brak," meaning "salty"...

 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
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...

. It is 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 Neritidae, the nerites.

Theodoxus fluviatilis is the type species
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...

 of the genus Theodoxus. Anistratenko (2005) designated the lectotype
Lectotype
In botanical nomenclature and zoological nomenclature, a lectotype is a kind of name-bearing type. When a species was originally described on the basis of a name-bearing type consisting of multiple specimens, one of those may be designated as the lectotype...

 for Theodoxus fluviatilis.

Subspecies

Several subspecies are (inconsistently) recognized by various authors:
  • Theodoxus fluviatilis fluviatilis (Linnaeus, 1789) - it has been described from freshwater
  • Theodoxus fluviatilis fluviatilis f. fontinalis Brard, 1815 or as a synonym of Theodoxus fluviatilis
  • Theodoxus fluviatilis littoralis (Linnaeus, 1789) - it has been described from brackish water, or as a synonym of Theodoxus fluviatilis
  • Theodoxus fluviatilis sardous (Menke, 1830)
  • Theodoxus fluviatilis subthermalis Issel, 1865 - or Theodoxus subthermalis (Bourguignat in Issel, 1865)
  • Theodoxus fluviatilis thermalis (Dupuy, 1851)
  • Theodoxus fluviatilis transversetaeniatus A. J. Wagner, 1928
  • Theodoxus fluviatilis dalmaticus Sow. - in Lake Ohrid
    Lake Ohrid
    Lake Ohrid straddles the mountainous border between the southwestern Macedonia and eastern Albania. It is one of Europe's deepest and oldest lakes, preserving a unique aquatic ecosystem with more than 200 endemic species that is of worldwide importance...

  • Theodoxus fluviatilis euxinus (Clessin, 1885) has been considered as a subspecies - see Theodoxus euxinus
    Theodoxus euxinus
    Theodoxus euxinus is a species of freshwater snail with a gill and an operculum. It is an aquatic gastropod mollusk in the family Neritidae, the nerites.- Distribution :Distribution of this species include:* Ukraine* Romania* Greece...

    (Clessin, 1886)


Bunje (2005) does not consider Theodoxus velox Anistratenko, 1999 to be a distinct species from Theodoxus fluviatilis.

Distribution

The distribution of this species is Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

an. Its distribution is scattered in Europe and in Western Asia except the Alps
Alps
The Alps is one of the great mountain range systems of Europe, stretching from Austria and Slovenia in the east through Italy, Switzerland, Liechtenstein and Germany to France in the west....

 and regions immediately north of the Alps. It does not live in Norway. Theodoxus fluviatilis has the most widespread distribution of all species in the genus Theodoxus.

Western Europe:

Central Europe:
  • Austria - non-indigenous, Danube near Tulln, Lower Austria
    Lower Austria
    Lower Austria is the northeasternmost state of the nine states in Austria. The capital of Lower Austria since 1986 is Sankt Pölten, the most recently designated capital town in Austria. The capital of Lower Austria had formerly been Vienna, even though Vienna is not officially part of Lower Austria...

    , since 2001
  • Czech Republic - extinct in Bohemia. The only findings were in the Elbe
    Elbe
    The Elbe is one of the major rivers of Central Europe. It rises in the Krkonoše Mountains of the northwestern Czech Republic before traversing much of Bohemia , then Germany and flowing into the North Sea at Cuxhaven, 110 km northwest of Hamburg...

     river near Litoměřice
    Litomerice
    Litoměřice is a town at the junction of the rivers Elbe and Ohře in the north part of the Czech Republic, approximately 64 km northwest of Prague....

     in 1917. The most recent findings of empty shells were in 1943.
  • Germany - high endangered (Stark gefährdet)
  • Poland
  • Slovakia - non-indigenous


Northern Europe:
  • Denmark
  • Sweden - up to 58° N
  • Åland Islands
    Åland Islands
    The Åland Islands form an archipelago in the Baltic Sea. They are situated at the entrance to the Gulf of Bothnia and form an autonomous, demilitarised, monolingually Swedish-speaking region of Finland...

     - known alive there since 1994 (belongs to Finland)


Eastern Europe:
  • Estonia
  • Lithuania
  • Latvia
  • Belarus
  • western Russia
  • Gulf of Odessa
    Gulf of Odessa
    Gulf of Odessa, or Odessa Bay, is a part of the Black Sea between cape E in North and Cape Velyky Fontan in South. The coasts of the gulf have capes Langeron and Malyi Fontan...

     - since 1997
  • Ukraine - non-indigenous, first record in 1955

Southern Europe:
  • Croatia
  • Lake Ohrid
    Lake Ohrid
    Lake Ohrid straddles the mountainous border between the southwestern Macedonia and eastern Albania. It is one of Europe's deepest and oldest lakes, preserving a unique aquatic ecosystem with more than 200 endemic species that is of worldwide importance...

    , Macedonia - subspecies Theodoxus fluviatilis dalmaticus
  • Albania (cf. lake Ohrid is between Albania/Macedonia)
  • mainland Greece and Crete
    Crete
    Crete is the largest and most populous of the Greek islands, the fifth largest island in the Mediterranean Sea, and one of the thirteen administrative regions of Greece. It forms a significant part of the economy and cultural heritage of Greece while retaining its own local cultural traits...



Asia:

Bunje (2005) hypothetized that the ancestral range of Theodoxus fluviatilis was the Ponto
Black Sea
The Black Sea is bounded by Europe, Anatolia and the Caucasus and is ultimately connected to the Atlantic Ocean via the Mediterranean and the Aegean seas and various straits. The Bosphorus strait connects it to the Sea of Marmara, and the strait of the Dardanelles connects that sea to the Aegean...

-Pannonian region (southern Ukraine, Romania and Hungary). Firstly it colonized northern Italy, Greece and Turkey; in the second phase it colonized Spain, France and Germany. Finally in the Holocene
Holocene
The Holocene is a geological epoch which began at the end of the Pleistocene and continues to the present. The Holocene is part of the Quaternary period. Its name comes from the Greek words and , meaning "entirely recent"...

 it colonized the British Isles, Sweden and the Baltic Sea.

Shells of Theodoxus fluviatilis have also been found in the following sites:
  • Upper Paleolithic
    Upper Paleolithic
    The Upper Paleolithic is the third and last subdivision of the Paleolithic or Old Stone Age as it is understood in Europe, Africa and Asia. Very broadly it dates to between 40,000 and 10,000 years ago, roughly coinciding with the appearance of behavioral modernity and before the advent of...

     archaeological site in the cave Caldeirão, Pedreira (Tomar), Tomar Municipality, Portugal.
  • about 6000 years B.P. in Litorina age on Åland Islands

Description

Theodoxus fluviatilis was originally described (under the name Nerita fluviatilis) by Carl Linnaeus in 1758. Linnaeus's original text (the type description) is very short, and reads as follows:
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 depressed, strongly calcified and with three whorls. It is basically whitish or yellowish with dark reddish or violetish reticulate pattern, very variably arranged (adapted to environmental factors), sometimes partly in bands, occasionally evenly dark. It is very variable in colors and in color patterns (it has great polymorphism
Polymorphism (biology)
Polymorphism in biology occurs when two or more clearly different phenotypes exist in the same population of a species — in other words, the occurrence of more than one form or morph...

 in colors). In the Mediterranean region there are slightly different forms. The shell may be corroded. 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...

 is light reddish with red margin, with broad rib and without apophysis
Apophysis
Apophysis is an open source fractal flame editor and renderer for Microsoft Windows.Apophysis has many features for creating and editing fractal flames, including an editor which allows one to directly edit the transforms by manipulating triangles, a mutations window, which applies random edits to...

.

The width of the shell is 5-9 mm, up to 11 mm or up to 13 mm. The height of the shell is 4-6.5 mm, or up to 7 mm.

The maximum width of the shell of freshwater population is 13.1 mm. The maximum height of the shell of freshwater population is 9.3 mm. The maximum weight of the shell is 343 mg.

The maximum width of the shell of brackish water population is 9.3 mm. The maximum height of the shell of brackish water population is 5.8 mm. The maximum weight of the shell is 124 mg.

The animal is light yellow with head black. Tentacles are greyish and long. Eyes are big and black, foot is whitish.

Ecology

This small snail inhabits the central and lower parts of rivers (up to 13 m deep), also in brackish water
Brackish water
Brackish water is water that has more salinity than fresh water, but not as much as seawater. It may result from mixing of seawater with fresh water, as in estuaries, or it may occur in brackish fossil aquifers. The word comes from the Middle Dutch root "brak," meaning "salty"...

 in tidal river
Tidal river
A tidal river is a river, or more typically a stretch of a river, whose flow and level is influenced by tides. An example of a tidal river is the portion of the Connecticut River flowing from Windsor Locks, Connecticut, to the Atlantic Ocean. The Brisbane River, which flows into the Pacific Ocean...

s of the estuary
Estuary
An estuary is a partly enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea....

. Sometimes it lives in lakes on unvegetated bottom. It rarely lives in springs (rheocrenes), in ground water and in caves. For example there was pH
PH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...

 7.8-8.9 in lakes in Åland Islands with Theodoxus fluviatilis.

The ability of Theodoxus fluviatilis to live in freshwater and also in brackish water is a representation of phenotypic plasticity
Phenotypic plasticity
Phenotypic plasticity is the ability of an organism to change its phenotype in response to changes in the environment. Such plasticity in some cases expresses as several highly morphologically distinct results; in other cases, a continuous norm of reaction describes the functional interrelationship...

 of this species. It can live up to 60 m depth in coastal waters. Brackish water populations can live in salinity
Salinity
Salinity is the saltiness or dissolved salt content of a body of water. It is a general term used to describe the levels of different salts such as sodium chloride, magnesium and calcium sulfates, and bicarbonates...

 up to 15 ‰ in the Baltic Sea or up to 18 ‰ in the Baltic Sea and in the Black Sea
Black Sea
The Black Sea is bounded by Europe, Anatolia and the Caucasus and is ultimately connected to the Atlantic Ocean via the Mediterranean and the Aegean seas and various straits. The Bosphorus strait connects it to the Sea of Marmara, and the strait of the Dardanelles connects that sea to the Aegean...

. Populations from brackish water tolerates higher salinity than populations from freshwater. Brackish water populations have much higher accumulation of ninhydrin
Ninhydrin
Ninhydrin is a chemical used to detect ammonia or primary and secondary amines. When reacting with these free amines, a deep blue or purple color known as Ruhemann's purple is produced...

-positive substances in the foot.

This species requires a stony substrate. It lives on pebbles, sometimes on boulders and rarely on dead wood. It tolerates mild organic pollution, low oxygen content (down to below 2 mg/liter) but does not tolerate long periods of droughts or ice. It lives in mesotrophic waters, sometimes in oligotrophic. Theodoxus fluviatilis has large phenotypic plasticity
Phenotypic plasticity
Phenotypic plasticity is the ability of an organism to change its phenotype in response to changes in the environment. Such plasticity in some cases expresses as several highly morphologically distinct results; in other cases, a continuous norm of reaction describes the functional interrelationship...

 and it was found to be living on stones and on the dead wood in freshwater environment; while it lives on stones and on Fucus vesiculosus, Potamogeton
Potamogeton
Potamogeton is a genus of aquatic, mostly freshwater, plants of the family Potamogetonaceae. Most are known by the common name pondweed, although many unrelated plants may be called pondweed, such as Canadian pondweed...

spp. and Zostera marina
Zostera marina
Zostera marina is a species of seagrass known by the common names common eelgrass and seawrack. It is an aquatic plant native to marine environments on the coastlines of mostly northern sections of North America and Eurasia. It is the most wide-ranging marine flowering plant in the Northern...

in brackish water in the Baltic Sea
Baltic Sea
The Baltic Sea is a brackish mediterranean sea located in Northern Europe, from 53°N to 66°N latitude and from 20°E to 26°E longitude. It is bounded by the Scandinavian Peninsula, the mainland of Europe, and the Danish islands. It drains into the Kattegat by way of the Øresund, the Great Belt and...

. It can also occur on aggregates of Mytilus
Mytilus
Mytilus was an Illyrian king of the Dardanian Kingdom. Mytilus is probably the son of Monunius.Mytilus is the second Illyrian monarch to have struck in 270 BC coins bearing his name after Monunius...

.Theodoxus fluviatilis together with the isopod Saduria entomon
Saduria entomon
Saduria entomon is a benthic isopod crustacean of the family Chaetiliidae. It is distributed along the coasts of the Arctic Ocean and of the northern Pacific Ocean. It is also found in the brackish Baltic Sea, where it is considered a glacial relict. Moreover it is present in a number of North...

has been found to be a dominant part of the fauna biomass
Biomass (ecology)
Biomass, in ecology, is the mass of living biological organisms in a given area or ecosystem at a given time. Biomass can refer to species biomass, which is the mass of one or more species, or to community biomass, which is the mass of all species in the community. It can include microorganisms,...

 in the central and northern Baltic Sea. Brackish water populations can reach densities
Population density
Population density is a measurement of population per unit area or unit volume. It is frequently applied to living organisms, and particularly to humans...

 up to 200-1000 snails per m². Theodoxus fluviatilis dalmaticus in Lake Ohrid
Lake Ohrid
Lake Ohrid straddles the mountainous border between the southwestern Macedonia and eastern Albania. It is one of Europe's deepest and oldest lakes, preserving a unique aquatic ecosystem with more than 200 endemic species that is of worldwide importance...

 can reach population densities up to 6412 snails per m².

It feeds on algae cover and diatoms on stones.

Sexes are separate (dioecious
Dioecious
Dioecy is the property of a group of biological organisms that have males and females, but not members that have organs of both sexes at the same time. I.e., those whose individual members can usually produce only one type of gamete; each individual organism is thus distinctly female or male...

) and cross-fertilization
Cross-fertilization
Cross-fertilization can refer to:*Allogamy, where an ovum from one individual is fertilized with the spermatozoa of another*Heterosis, where different strains are cross-bred to form a hybrid...

 occurs. There is unique structure of the flagellum
Flagellum
A flagellum is a tail-like projection that protrudes from the cell body of certain prokaryotic and eukaryotic cells, and plays the dual role of locomotion and sense organ, being sensitive to chemicals and temperatures outside the cell. There are some notable differences between prokaryotic and...

 of spermatozoon
Spermatozoon
A spermatozoon is a motile sperm cell, or moving form of the haploid cell that is the male gamete. A spermatozoon joins an ovum to form a zygote...

: the flagellum is divided into two parts. Eggs are laid in an egg mass from mid-April to October. There are less than 10 eggs. Only one egg develops and other eggs serve as nutrition for the embryo.

0.5-1 mm sized juveniles hatch after 30 days (in 25°C) or after 65 days (in 20°C). Sexual maturity is in less than 1 year. The life span is 2-3 years.

Parasites of Theodoxus fluviatilis include:
  • The trematode Plagioporus skrjabini
    Plagioporus skrjabini
    Plagioporus skrjabini is a species of a trematode in the family Opecoelidae.- Hosts :Hosts of Plagioporus skrjabini include:* Snail Theodoxus fluviatilis serves as the first intermediate host...

    - Theodoxus fluviatilis serves as the first intermediate host
    Intermediate host
    A secondary host or intermediate host is a host that harbors the parasite only for a short transition period, during which some developmental stage is completed. For trypanosomes, the cause of sleeping sickness, humans are the primary host, while the tsetse fly is the secondary host...



This species is threatened mainly by river engineering
River engineering
River engineering is the process of planned human intervention in the course, characteristics or flow of a river with the intention of producing some defined benefit. People have intervened in the natural course and behaviour of rivers since before recorded history - to manage the water resources,...

, and water pollution
Water pollution
Water pollution is the contamination of water bodies . Water pollution occurs when pollutants are discharged directly or indirectly into water bodies without adequate treatment to remove harmful compounds....

 in densely populated regions.

External links

  • Bondesen P. (1940). "Preliminary investigations into the development of Neritina fluviatilis L. in brackish and fresh waters". Videnskabelige Meddelelser fra Dansk Naturhistorisk Forening 104: 283-318.
  • Boycott A. E. (1936). "Neritina fluviatilis in Orkney". Journal of Conchology 20: 199-200.
  • Kangas P. & Skoog G. (1978). "Salinity tolerance of Theodoxus fluviatilis (Mollusca, Gastropoda) from freshwater and from different salinity regimes in the Baltic Sea". Estuarine and Coastal Marine Science 6: 409-416. doi:10.1016/0302-3524(78)90131-7.
  • Lumbye J. (1958). "The oxygen consumption of Theodoxus fluviatilis (L.) and Potamopyrgus jenkinsi (Smith) in brakish and fresh water". Hydrobiologia
    Hydrobiologia
    Hydrobiologia: The International Journal of Aquatic Sciences is a scientific journal specialising in hydrobiology, including limnology and oceanography, systematics of aquatic organisms and aquatic ecology.-History:...

    10(1): 245-262. doi:10.1007/BF00142190.
  • Skoog G. (1971). "Variations in the distribution of Theodoxus fluviatilis on stony locations in the northern Baltic proper". Thalassia Jugoslavica 7: 363-372. Weichtier des Jahres 2004. Mollusc of the year 2004 (in Germany).
  • Örstan A. (2007). "New year, new snail: Theodoxus fluviatilis". Snail's tales. - with photos of eggs and view inside the shell with resorbed columella.
  • 1862 drawing of Theodoxus fluviatilis
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