Overview

Distribution

Theodoxus fluviatilis is considered holarctic, occurring in both the Nearctic and Palearctic biogeographic regions. However, they are more commonly seen in the Palearctic region, spreading far west to England, and east into southwestern Asia. Many patches within Europe are uninhabited, mainly the mountainous regions. This snail's ability to survive in freshwater allowed for migration throughout Eastern Europe, and later re-entry into the brackish waters of the Baltic Sea.

Biogeographic Regions: nearctic (Introduced ); palearctic (Native )

Other Geographic Terms: holarctic

  • Bunje, P. 2005. Pan-European phylogeography of the aquatic snail Theodoxus fluviatilis (Gastropoda: Neritidae). Molecular Ecology, 14: 4323-4340. Accessed May 23, 2011 at http://paulbunje.com/pdfs/Bunje2005.pdf.
  • Symanowski, F., J. Hildebrandt. 1984. Differences in osmotolerance in freshwater and brackish water populations of Theodoxus fluviatilis (Gastropoda: Neritidae) are associated with differential protein expression. Journal of Comparative Physiology, 180 (3): 337-346.
  • Zettler, M., J. Frankowski, R. Bochert, M. Rohner. 2004. Morphological and ecological features of Theodoxus fluviatilis (Linnaeus, 1758) from Baltic brackish water and German freshwater populations. Journal of Conchology, 38 (3): 305-316. Accessed May 11, 2011 at http://www.io-warnemuende.de/tl_files/bio/ag-benthische-organismen/pdf/zettler_et_al-2004-theodoxus.pdf.
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Range Description

This species is the most widely distributed species of the Theodoxus genus. The freshwater subspecies T. fluviatilis fluviatilis is widespread, with a Western Palaearctic range, occurring principally in the lowlands of northern, central and eastern Europe and southern Sweden to 60 degrees north. It is widespread in suitable habitats across Europe from western Russia eastwards to the Iberian peninsula and from the Balkan peninsula in the south to southern Scandinavia in the north (Zettler et al. 2004). The range of this species occurs as far as Ireland to the west (Lucey et al. 1992), and as far as the Scottish Orkney islands to the north (Zettler et al. 2004). It also occurs in lowland areas of Anatolia (Yildirim 1999). It is now expanding towards the Black Sea Basin and the Carpathian Basin where this species is invasive. There are large areas across Europe in which this species is absent, in particular in mountainous areas (Bunje 2005). This species is absent in Norway and is only present in Finland on the Åland islands (Zettler et al. 2004). It has also become extinct in the Czech Republic (Farkac et al. 2005).

The subspecies T. fluviatilis littoralis is present in the North Sea in brackish waters of the Orkney islands and the Netherlands, and in low salinity waters of the Baltic Sea (Zettler et al. 2004). It also occurs in the Black Sea in waters with a salt content below 18% (Butenko 2001).
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Widespread throughout Europe from the British Isles and Spain to the Caucasus and the Black Sea, and from the Baltic Sea to Italy.  Reported from Turkey (Bafra and Sinop on the southern coast of the Black Sea, Öktener, 2004), but these findings are probably the very similar Theodoxus  heldreichi (von Martens, 1879).     

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Physical Description

Morphology

Although difficult to distinguish between different species of Theodoxus, Theodoxus fluviatilis has a few main morphological features used for identification. These include size, color patterns of the periostracum, the operculum and the radula. The common river nerite has a soft-tissued body encased within a round, calcareous shell. This species is known to absorb the inner walls of the shell, thus allowing for a more spacious environment inside the shell. This absorption may allow more room for their food intake. The operculum, a hard, proteinaceous plate protecting the body when fully retracted within the shell, is light red with broad ribs. The margin of the operculum is red.

The species has an average mass of 50 mg, an average shell length of 9 mm, and an average shell width of 6 mm. The different specimens, marine and freshwater, show some morphological variances. Freshwater specimens tend to be larger and thicker than the marine forms. Freshwater specimens also have a yellowish-green color, while marine forms are mostly black. Since they are dioecious, the male and female sexes are separate. Both have reproductive organs. The male's penis is located on the right side of their body, near the base. The female reproductive organs are located inside the mantle cavity. Within the mantle cavity, females have two openings, one for fertilization and the other for discharging their eggs.

Range mass: .025 to .345 g.

Average mass: .050 g.

Average length: 9 mm.

Average wingspan: 6 mm.

Range basal metabolic rate: 1 to 8 cm3.O2/g/hr.

Average basal metabolic rate: 5 cm3.O2/g/hr.

Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry

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Ecology

Habitat

Commonly known as the river nerite, Theodoxus fluviatilis was first discovered in saltwater, originating in the Black Sea. Currently this species is mainly found in freshwater streams and rivers. The river nerite is also found along coastal regions of the Black and Baltic Seas, and also lives in estuaries, regions where freshwater rivers meet saltwater seas. Within this habitat, it lives on hard benthic substrates, typically rocks and submerged wood, and in calcium-rich waters. Theodoxus fluviatilis also lives as deep as 60 meters below the surface, and is sometimes found no higher than a centimeter above the water surface.

Average elevation: .01 m.

Range depth: 0 to 60 m.

Habitat Regions: temperate ; saltwater or marine ; freshwater

Aquatic Biomes: benthic ; lakes and ponds; rivers and streams; coastal ; brackish water

Other Habitat Features: estuarine

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Habitat and Ecology

Habitat and Ecology
This species can be found in rivers, larges lakes, estuarine section of rivers, brackish coastal waters and springs (within the Mediterranean part of the range). It requires a solid surface such as rocks, concrete, stones to be able to attach itself to. The species displays wide polymorphism in shell pattern and colour, making it difficult to identify (Anistratenko 2005).

Systems
  • Freshwater
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Depth range based on 36 specimens in 1 taxon.
Water temperature and chemistry ranges based on 1 sample.

Environmental ranges
  Depth range (m): 1 - 22
  Temperature range (°C): 8.600 - 8.600
  Nitrate (umol/L): 1.265 - 1.265
  Salinity (PPS): 7.618 - 7.618
  Oxygen (ml/l): 8.061 - 8.061
  Phosphate (umol/l): 0.326 - 0.326
  Silicate (umol/l): 11.134 - 11.134

Graphical representation

Depth range (m): 1 - 22
 
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.

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Marine to freshwater, under stones or wood in river systems of Europe, especially in running water.

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Trophic Strategy

As Theodoxus fluviatilis is an herbivore and a detritivore, it mainly feeds on phytoplankton (mainly diatoms), but also feeds on detritus and a variety of algae. Its radula is specialized to grind even the hardest phytoplankton, making it easier to digest. Detritus is the organic material that comes from dead or decomposing plants or animals. While developing, the larva will feed within the egg capsule.

Plant Foods: algae; phytoplankton

Other Foods: detritus

Foraging Behavior: filter-feeding

Primary Diet: herbivore (Algivore); detritivore

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Associations

Theodoxus fluviatilis plays an important role for the health and maintenance of large structuring macrophytes. They aid the growth of the perennial brown alga, Fucus vesiculosus. While other grazers inhibit the ability of Fucus to uptake nitrogen, T. fluviatilis does not, and thus aids in the growth of the algae. Not much is known about their symbiotic relationships with other animals.

  • Kautsky, L., S. Raberg. 2008. Grazer identity is crucial for facilitating growth of the perennial brown alga Fucus vesiculosus. Marine ecology process series, 361: 111-118.
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Because their hard calcareous shell completely covers their body, most predators avoid Theodoxus fluviatilis as a potential food source. Their eggshells are also calcified and hardened, thus protecting them when predators attack. However, a few known predators include the European perch, Perca flavescens, as well as two crayfishes, Orconectes limosus and Astacus astacus. These animals have adaptations that allow them to break through the snails' calcareous shell. Orconectes limosus, endemic to North America, is an invasive species in Europe.

Known Predators:

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Life History and Behavior

Behavior

Like many other gastropods, Theodoxus fluviatilis has a well-developed nervous system. Sense organs include eyes, statocysts, tactile organs, and chemoreceptors. Statocysts are fluid-filled cellular cysts used to sense direction of gravity, and thus sense equilibrium. Chemoreceptors are used to detect chemical stimuli. The snails also have a pair of eyes, each located at the end of their antennae that give them a visual sense perception of their habitat. Thus, they see their environment, sense movement, and also sense their state of balance.

Communication Channels: visual ; tactile ; chemical

Perception Channels: visual ; tactile ; chemical

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Life Cycle

Theodoxus fluviatilis develops in a similar manner as most other gastropods, however, the snail develops within the egg, so there is no larval form. The shell forms as the egg is developing. Initially, the mouth is anterior and the anus is posterior. However, after a process known as torsion, the positions of the body parts change.

Torsion involves two steps, each being a 90 degree rotation. The first rotation is caused by a contraction of the foot retractor muscle. It rotates the shell and visceral mass 90-degrees counterclockwise, leaving the anus on the right side of the body. The second rotation is caused by further development of differentiating tissues. This allows for the mantle cavity to develop near the anus and an additional 90-degree rotation, placing the anus directly above the head and mouth.

The positioning of the anus above the head would normally result in sanitary problems, with wastes washing directly over the gills. However, this is resolved by another process known as coiling. Coiling is not the same as torsion, however it can occur at the same time in development as torsion. Coiling of the shell and visceral mass allow for the loss of the gill, auricle, and kidney, all on the right side of the mantle cavity, and thus allow the snails to avoid sanitation problems. Since the water-flow through the mantle cavity is unidirectional, it flows into the left side and out of the right side, carrying with it wastes from the anus, which is near the right side. The single gill on the left side is then exposed only to clean water, avoiding any such sanitation problems. Once eggs hatch, they are considered miniature adults and take 18 months to fully mature into adult snails.

  • Orton, R., R. Sibley. 1990. Egg size and growth rate in Theodoxus fluviatilis (L). Functional Ecology, 4 (1): 91-94. Accessed May 22, 2011 at http://www.jstor.org/stable/2389657.
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Life Expectancy

Theodoxus fluviatilis lives in nature for approximately two to three years. Longevity in an aquarium kept at room temperature has been recorded as two years.

Range lifespan

Status: wild:
3.5 (high) years.

Range lifespan

Status: captivity:
2 (high) years.

Typical lifespan

Status: wild:
2 to 3 years.

Average lifespan

Status: captivity:
2 years.

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Reproduction

Theodoxus fluviatilis reproduces between April and October. These snails have separate sexes and reproduce sexually. The male reproductive organ is located on the right side of its body. The female reproductive organs are within the mantle cavity. In the mantle cavity, there are two openings, one for fertilization and another for discharging the eggs. Fertilization is internal. The nerites are oviparous, females laying calcified eggs, normally on benthic surfaces or on their shell near the opening.

Mating System: monogamous

Theodoxus fluviatilis are dioecious and oviparous. They are semelparous, producing offspring all at once, after which the parent usually dies. During their mating season, anywhere from 50 to 200 eggs are laid. These eggs are collectively known as a capsule, and only one of them contains an embryo. Each egg is made of two spherical halves, which split when newborns hatch. The rest are used as a food source for the newborns. Embryos usually take about 100 days to fully develop. Since they are involved in a biennial life cycle, their eggs hatch some time in the fall as miniature adults and fully mature 18 months later.

Breeding interval: They breed once in their lifetime, and they usually die after.

Breeding season: They breed between the warmer months of April and October.

Range number of offspring: 50 to 200.

Average age at sexual or reproductive maturity (female): 18 months.

Average age at sexual or reproductive maturity (male): 18 months.

Key Reproductive Features: semelparous ; sexual ; fertilization (Internal ); oviparous

Not much is known on the parental investment of T. fluviatilis, but some were found with their eggs attached to their shell near the opening. This could be some form of protection of the eggs from possible predators or even by providing nutrients to their young. The young are precocial when they hatch.

Parental Investment: precocial ; pre-hatching/birth (Provisioning: Female, Protecting: Female)

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Molecular Biology and Genetics

Molecular Biology

Barcode data: Theodoxus fluviatilis

The following is a representative barcode sequence, the centroid of all available sequences for this species.


There are 45 barcode sequences available from BOLD and GenBank.

Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.

See the BOLD taxonomy browser for more complete information about this specimen and other sequences.

ATGTTTGGTGTTTGATCAGGGTTAGTTGGAACTGCTTTAAGTTTGTTAATTCGAGCGGAACTTGGGCAGCCTGGTGCTTTATTAGGGGAT---GACCAGCTTTATAATGTAATTGTAACTGCTCATGCTTTTGTAATAATTTTTTTTCTTGTGATGCCTATAATAATTGGAGGTTTTGGTAATTGATTGGTTCCATTAATGTTAGGAGCTCCTGATATGGCATTTCCTCGGTTAAATAACATGAGTTTTTGGCTTCTTCCTCCNTCACTTACTTTATTGTTGGCTTCATCTGCAGTGGAAAGTGGGGTTGGTACTGGCTGAACTGTATACCCTCCTTTATCTGGAAATTTAGCTCATGCGGGAGGTTCTGTTGATTTAGCTATTTTTTCTCTACATTTGGCTGGTGTATCTTCTATTTTAGGGGCTGTTAATTTCATTACTACAATTATTAATATGCGATGACAAGGGATGCAATTTGAGCGATTGCCTTTATTTGTCTGATCTGTAAAAATTACTGCAATTTTATTATTATTATCTTTACCTGTGCTTGCTGGAGCAATTACTATACTATTAACTGATCGAAATTTTAATACTTCTTTTTTTGACCCTGCTGGTGGTGGTGATCCAATTTTATATCAGCACTTGGTTTGATTT
-- end --

Download FASTA File

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Statistics of barcoding coverage: Theodoxus fluviatilis

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 48
Specimens with Barcodes: 48
Species With Barcodes: 1
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Conservation

Conservation Status

Theodoxus fluviatilis are considered extinct in the Czech Republic. They are also endangered in Switzerland and Latvia, and considered in jeopardy in other European countries including the Netherlands and Slovenia. They are also protected under law in Latvia.

US Federal List: no special status

CITES: no special status

State of Michigan List: no special status

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IUCN Red List Assessment


Red List Category
LC
Least Concern

Red List Criteria

Version
3.1

Year Assessed
2012

Assessor/s
Kebapçı, U. & Van Damme, D.

Reviewer/s
Bohm, M., Collen, B. & Seddon, M.

Contributor/s
Seddon, M., Killeen, I., Offord, S., Duncan, C., Dyer, E., Soulsby, A.-M., Whitton, F., Kasthala, G., McGuinness, S., De Silva, R., Milligan, HT, Herdson, R., Thorley, J., Collins, A., McMillan, K. & Richman, N.

Justification
This is a widespread species which is both very common in certain parts of its range and is relatively tolerant to pollution; it is continuing to spread in the Danube drainage. Therefore it is assessed as Least Concern.

This species has been assessed at the regional level:
EU27 regional assessment: Least Concern (This species is categorised as Least Concern in the 27 member states of the European Union)
European regional assessment: Least Concern
Mediterranean regional assessment : Least Concern
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Population

Population
In some parts of its range this species is known to be very common (Zettler et al. 2004). The trends are unknown over the range, but some countries report a decline. In other parts of the region it is expanding, for example in the Danube in western Slovakia (Čejka et al. 2006). The species has a life span of 2-3 years and the eggs are laid from mid-April to October, with juveniles hatching after 30 - 60 days.

Population Trend
Stable
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Threats

Major Threats
The principal threats to the species are pollution of its habitats through eutrophication or other chemical sources, alteration of water courses, changes to flow regimes, and over-frequent dredging, however these threats don't seem to create major declines in the species. Mouthon (1996) showed that T. fluviatilis was relatively insensitive to biodegradable pollution. In the Danube, where it is an invasive species, it is replacing the original Theodoxus spp., as it seems to tolerate the polluted waters.
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Management

Conservation Actions

Conservation Actions
There are no conservation efforts known for this species.

In Red Lists of Latvia, Italy, UK, and the Republic of Ireland it is viewed as Least Concern. In The Netherlands it was considered to be Vulnerable. In Switzerland the species was considered to be highly threatened (CR equivalent), and in Czech Republic it is listed as Extinct (Farkac et al. 2005).
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Relevance to Humans and Ecosystems

Benefits

There are no known adverse effects of Theodoxus fluviatilis on humans.

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There are no known positive effects of Theodoxus fluviatilis on humans.

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Wikipedia

Theodoxus fluviatilis

Theodoxus fluviatilis, common name the river nerite, is a species of small freshwater and brackish water snail with a gill and an operculum, an aquatic gastropod mollusk in the family Neritidae, the nerites.[12]

It is widely distributed neritid snail occurring from Europe to Central Asia. It has a thick shell with an calcified operculum. The coloration pattern on the shell is very variable. It lives in freshwater and in brackish waters: in rivers and in lakes on stones. It is grazing on biofilms and diatoms are its main food source. Some if its populations are spreading and it can reach densities of thousands of snails per square meter. Females lay egg capsules with number of eggs, but only one snail hatches from the capsule.

Taxonomy[edit]

Theodoxus fluviatilis is the type species of the genus Theodoxus.[5] Anistratenko (2005)[5] designated the lectotype for Theodoxus fluviatilis.[5]

Subspecies[edit]

Several subspecies are (inconsistently) recognized by various authors:

  • Theodoxus fluviatilis fluviatilis (Linnaeus, 1789)[13][14][2] - it has been described from freshwater[15]
  • Theodoxus fluviatilis fluviatilis f. fontinalis Brard, 1815[13] or as a synonym of Theodoxus fluviatilis[2]
  • Theodoxus fluviatilis littoralis (Linnaeus, 1789)[13] - it has been described from brackish water,[15] or as a synonym of Theodoxus fluviatilis[2]
  • Theodoxus fluviatilis sardous (Menke, 1830)[2]
  • Theodoxus fluviatilis subthermalis Issel, 1865[2] - or Theodoxus subthermalis (Bourguignat in Issel, 1865)[9]
  • Theodoxus fluviatilis thermalis (Dupuy, 1851)[2]
    Theodoxus fluviatilis thermalis Syntype MHNT
  • Theodoxus fluviatilis transversetaeniatus A. J. Wagner, 1928[2]
  • Theodoxus fluviatilis dalmaticus Sow. - in Lake Ohrid[16]
  • Theodoxus fluviatilis euxinus (Clessin, 1885) has been considered as a subspecies[14] - see Theodoxus euxinus (Clessin, 1886)[2]

Bunje (2005)[11] does not consider Theodoxus velox Anistratenko, 1999[8] to be a distinct species from Theodoxus fluviatilis.[11]

Distribution[edit]

The distribution of this species was considered as European,[17] but it is western- to Central-Palaearctic.[18] Its distribution is scattered in Europe and in Western Asia[5] except the Alps and regions immediately north of the Alps.[10] It does live neither in Norway[10][15] not to Siberia.[18] Theodoxus fluviatilis has the most widespread distribution of all species in the genus Theodoxus.[11] It is one the most widely distributed species of Neritidae.[19]

This species is threatened mainly by river engineering, and water pollution in densely populated regions.[10] Population trend is stable, but in some areas it is declining, while in some areas it is expanding (in Danube river).[1]

Theodoxus fluviatilis nearly extinct in the Rhine river in 1970s because of water pollution.[19] The water quality has imporoved and the population has recovered but it had extinct in the Rhine in the late 1990s for an unknown reason.[19] It recolonized the Rhine probably by ship transport through Main-Danube Canal since 2006.[19] Based on cytochrome-c oxidase I (COI) gene it was shown, that the recolonization originated probably the Danube.[19]

The exact type locality is unknown, but it is probably the Main river in Southern Germany.[20][5]

Western Europe:

Central Europe:

Northern Europe:

Eastern Europe:

Southern Europe:

Asia:

There are records of Theodoxus fluviatilis Morocco and Algeria in northwestern Africa and some authors consider them as realiable.[18] But Brown (1994) recognized three species (Theodoxus numidicus, Theodoxus maresi, Theodoxus meridionalis) instead of Theodoxus fluviatilis in northwestern Africa.[39]

Bunje (2005)[11] hypothetized that the ancestral range of Theodoxus fluviatilis was the Ponto-Pannonian region (southern Ukraine, Romania and Hungary).[11] Firstly it colonized northern Italy, Greece and Turkey; in the second phase it colonized Spain, France and Germany.[11] Finally in the Holocene it colonized the British Isles, Sweden and the Baltic Sea.[11]

Shells of Theodoxus fluviatilis have also been found in the following sites:

Description[edit]

Theodoxus fluviatilis was originally described (under the name Nerita fluviatilis) by Carl Linnaeus in 1758. Linnaeus's original text (the type description) was very short, and reads as follows:[3]

The shell is depressed, strongly calcified and with three whorls.[21][41] 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.[10] It is very variable in colors and in color patterns (it has great polymorphism in colors).[5] In the Mediterranean region there are slightly different forms.[10] Larger shells are usually corroded.[30][15]

The width of the shell is 5-9 mm,[10] up to 11 mm[27] or up to 13 mm.[10] The height of the shell is 4-6.5 mm,[10] or up to 7 mm.[27]

The maximum width of the shell of freshwater population is 13.1 mm.[15] The maximum height of the shell of freshwater population is 9.3 mm.[15] The maximum weight of the shell is 343 mg.[15]

The maximum width of the shell of brackish water population is 9.3 mm.[15] The maximum height of the shell of brackish water population is 5.8 mm.[15] The maximum weight of the shell is 124 mg.[15]

Five views of a shell of Theodoxus fluviatilis.
Coloration and pattern is variable: two views of a shell of Theodoxus fluviatilis from Krokees, Greece.[38]

The calcified operculum is D-shaped, light reddish with red margin, with broad rib (also called ridge) on the inner side of the operculum.[10][20] The columellar muscle is attached to the rib.[20]

An outer side of an operculum.
An inner side of an operculum.

The animal is light yellow with head black.[10] Tentacles are greyish and long.[10] Eyes are big and black, foot is whitish.[10]

One row of teeth in the radula of Theodoxus fluviatilis. All Neritidae have rhipidoglossan radula (many small marginal teeth).[39]
Drawing of the reproductive system of a male by Lehmann (1873)[42] shows testis (on the left), prostate, vas deferens and penis (on the right).
Drawing of the reproductive system as firstly described (correctly) by Gustave Gilson (1896)[43] of a female shows:
1 - ovarium
2 - oviduct
3 - uterus
4 - diverticulum
5 - connection between bursa copulatrix and uterus
6 - receptaculum seminis
7 - bursa copulatrix
8 - vagina.

Ecology[edit]

Habitat[edit]

This small snail inhabits the central and lower parts of rivers (up to 13 m deep),[10] also in brackish water[10] in tidal rivers of the estuary.[21] Sometimes it lives in lakes on unvegetated bottom.[21] It rarely lives in springs (rheocrenes), in ground water and in caves.[21] For example there was pH 7.8-8.9 in lakes in Åland Islands with Theodoxus fluviatilis.[31] There was pH 7.0-8.4 in streams and rivers in Ireland with Theodoxus fluviatilis.[22]

It is swiftly attached to stones, that allows it to live in fast running waters and in wave zone in lakes.[30] The ability of Theodoxus fluviatilis to live in freshwater and also in brackish water is a representation of phenotypic plasticity of this species.[11] It can live up to 60 m depth in coastal waters.[15] Brackish water populations can live in salinity up to 15 ‰ in the Baltic Sea[13][28] or up to 18 ‰ in the Baltic Sea and in the Black Sea.[11] Populations from brackish water tolerates higher salinity than populations from freshwater.[15] Brackish water populations have much higher accumulation of ninhydrin-positive substances in the foot.[44]

This species requires a stony substrate.[10] It lives on pebbles, sometimes on boulders and rarely on dead wood.[21] It tolerates mild organic pollution, low oxygen content (down to below 2 mg/liter) but does not tolerate long periods of droughts or ice.[10] It lives in mesotrophic waters, sometimes in oligotrophic.[21] It is an indicator species for river monitoring (in Germany), but spreading populations have also high tolerance to degraded habitats.[19] Theodoxus fluviatilis has large phenotypic plasticity 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 spp. and Zostera marina in brackish water in the Baltic Sea.[15] It can also occur on aggregates of Mytilus.[15] Theodoxus fluviatilis together with the isopod Saduria entomon has been found to be a dominant part of the fauna biomass in the central and northern Baltic Sea.[45] Brackish water populations can reach densities up to 200-1000 snails per m².[15] Theodoxus fluviatilis dalmaticus in Lake Ohrid can reach population densities up to 6412 snails per m².[16] It was found population density up to 9000 snails per m² in a spring of Anços river in Central Portugal, where there is a stable temperature 15.3-16.6°C, that allows continuous reproduction to Theodoxus fluviatilis.[24]

Feeding habits[edit]

Theodoxus fluviatilis feeds on diatoms on stones mainly.[30][15] It is scrapping biofilms and it consume detritus.[24] It can also consume Cyanobacteria and green algae as a poor food supply.[30] Cyanobacteria have toxins and indigestible mucopolysaccharides, and green algae have cellulose in their cell walls (Theodoxus species has no cellulase enzymes to digest cellulose).[30]

Peters & Traunspurger (2012) studied the effect of grazing of Theodoxus fluviatilis on epilithic meiofauna and algae.[46]

Life cycle[edit]

Lateral view of a corroded shell of Theodoxus fluviatilis. The width of this shell is 8 mm and the height of the shell is 6 mm. There are remnants of two egg capsules.

Sexes are separate (dioecious) and cross-fertilization occurs.[21] The sex ratio is 1:1.[30] There is unique structure of the flagellum of spermatozoon: the flagellum is divided into two parts.[47]

Eggs are laid in an egg capsules[21] from mid-April to October[10] in temperatures above 10°C[30] on stones and sometimes on shells of shells of other Theodoxus fluviatilis.[48] The female usually lay a cluster of 4-5 capsules.[30] One female will usually lay about 40 capsules in summer and about 20 capsules in autumn.[30] The fresh capsule is white.[30] The older capsule is yellow or brown and there may be epiphyton on the surface of the capsule.[30] The size of the capsule is 0.9-1.1 mm in diameter.[30] Capsules in brackish water are small with about 0.8 mm in diameter. There are sometimes laid empty sterile small capsules 0.5–0.8 mm in diameter.[30]

There are 100–200 eggs in each capsule in freshwater and 55-80 eggs in each capsule in brackish water.[30] Only one egg develops and other eggs serve as nutrition for the embryo,[49] therefore only one juvenile snail will hatch from each capsule.[30]

Juveniles with a shell length 0.5-1 mm hatch after 30 days (in 25°C) or after 65 days (in 20°C).[13][10] Ash-free dry weight of newly hatched snails is 0.012 mg.[30] The protoconch has one whorl.[20] Capsules from spring are hatching after 2-3 months in August–September.[30] Capsules from late summer are overwintering, the embryo development is ceased in temperatures below 10°C and they are hatching after 7-8 months in spring.[30]

The shell is growing mainly from May to August and there is no shell growth in winter.[30] Sexual maturity is in less than 1 year,[21] when the shell length is 5.5–5.7 mm.[30]

The life span is 2-3 years.[10] Age of few snails was estimated to 3.5 years.[30] The mortality rate is low in summer.[30] The mortality rate is higher in winter because ice and storms cause movement of the substratum, that cause mechanical damage to snails.[30]

Parasites[edit]

Parasites of Theodoxus fluviatilis include:

Predators of Theodoxus fluviatilis include:

References[edit]

This article incorporates public domain text from references[3][10]

  1. ^ a b c d e f g h i j k l m n Kebapçı U. & Van Damme D. (2012). "Theodoxus fluviatilis". The IUCN Red List of Threatened Species. Version 2014.2. <www.iucnredlist.org>. Downloaded on 30 July 2014.
  2. ^ a b c d e f g h i j "Theodoxus (Theodoxus) fluviatilis". Fauna Europaea, last update 27 January 2011, accessed 12 April 2011.
  3. ^ a b c Linnaeus C. (1758). Systema Naturae per regna tria naturae, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. 10th edition. Vermes. Testacea: 700-781. Holmiae. (Salvius). page 777.
  4. ^ (German) Lindholm W. A. (1908). "Materialien zur Molluskenfauena [sic] von Südwestrussland, Polen und der Krim". Zapiski Novorossijskago Obshchestva Estestvoispytatelej - Mémoires de la Société des Naturalistes de la Nouvelle-Russie 31: 199-232. Odessa.
  5. ^ a b c d e f g h Anistratenko V. V. (2005). "Lectotypes for Tricolia pullus, Gibbula divaricata and Theodoxus fluviatilis (Mollusca, Gastropoda) revisited". Vestnik zoologii 39(6): 3-10. PDF .
  6. ^ "Species in genus Theodoxus" (n=20). AnimalBase, accessed 11 April 2011.
  7. ^ (French) Montfort P. D. de (1810). Conchyliologie systématique, et classification méthodique des coquilles; offrant leurs figures, leur arrangement générique, leurs descriptions caractéristiques, leurs noms; ainsi que leur synonymie en plusieurs langues. Ouvrage destiné à faciliter l'étude des coquilles, ainsi que leur disposition dans les cabinets d'histoire naturelle. Coquilles univalves, non cloisonnées. Tome second. - pp. [1-3], 1-676. Paris. page 351.
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