Theodoxus is a genus

Genus

In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 of small 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"...

 neritid

Neritidae

Neritidae, common name the nerites, is a taxonomic family of small to medium-sized saltwater and freshwater snails which have a gill and a distinctive operculum, marine, brackish water and freshwater gastropod mollusks in the order Neritoida....

 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 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...

.

Distribution

Distribution of the genus Theodoxus include Europe and northern Africa to southern Iran.

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 semiovular with flat apertural plain. There is umbilicus. The columella and inner 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...

 are dissolved.

Species in the genus Theodoxus are highly variable in size, pattern of color of the periostracum

Periostracum

The periostracum is a thin organic coating or "skin" which is the outermost layer of the shell of many shelled animals, including mollusks and brachiopods. Among mollusks it is primarily seen in snails and clams, i.e. in bivalves and gastropods, but it is also found in cephalopods such as the...

, 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...

 and the radula

Radula

The radula is an anatomical structure that is used by molluscs for feeding, sometimes compared rather inaccurately to a tongue. It is a minutely toothed, chitinous ribbon, which is typically used for scraping or cutting food before the food enters the esophagus...

 that makes identification very difficult.

Ecology

Animals are attached to stones, often also under stones, in up to 5-6 m depth or deeper, feeding on algae covers. Theodoxus needs rough surfaces to be able to digest its food, so stony substrate is necessary. Green algae are not consumed, Theodoxus has no cellulase

Cellulase

400px|thumb|right|alt = Colored dice with checkered background|Ribbon representation of the Streptomyces lividans beta-1,4-endoglucanase catalytic domain - an example from the family 12 glycoside hydrolases...

s. Animals lay egg capsules containing 30-70 eggs each, usually on the shells of other Theodoxus animals. Only 1 juvenile grows, the other eggs serve as food.

Species

Species within the genus Theodoxus include:

subgenus Theodoxus

• Theodoxus altenai
  Theodoxus altenai
  Theodoxus altenai 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 Antalya Province, southern Turkey....
  
  Schütt, 1965
• Theodoxus baeticus (Lamarck, 1822)
• Theodoxus danubialis
  Theodoxus danubialis
  Theodoxus danubialis is a small species of freshwater snail with an operculum. It is an aquatic gastropod mollusk in the family Neritidae, the nerites.- Distribution :Distribution of this species is Mediterranean and Pontic.* Serbia* Croatia...
  
  (Pfeiffer, 1828)
• Theodoxus elongatulus (Morelet, 1845)
• 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)
• Theodoxus fluviatilis
  Theodoxus fluviatilis
  Theodoxus fluviatilis, common name the river nerite, is a small species of freshwater and brackish water snail with a gill and an operculum. It is an aquatic gastropod mollusk in the family Neritidae, the nerites....
  
  (Linnaeus, 1758) - 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...
  
  . synonyms: Theodoxus brauneri (Lindholm, 1908) (but as separate species per); Theodoxus brauneri f. lacrymans Lindholm, 1908; Theodoxus brauneri f. alboguttata Lindholm, 1908; Theodoxus brauneri f. pulherrima Lindholm, 1908; Theodoxus lutetianus Montfort, 1810. Bunje (2005) does not consider Theodoxus velox Anistratenko, 1999 to be a distinct species from Theodoxus fluviatilis.
• Theodoxus heldreichi (Martens, 1879)
• Theodoxus hispalensis (Martens, 1879)
• Theodoxus meridionalis
  Theodoxus meridionalis
  Theodoxus meridionalis 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 :...
  
  (Philippi, 1836)
• Theodoxus pallasi Lindholm, 1924
• Theodoxus prevostianus (Pfeiffer, 1828)
• Theodoxus saulcyi (Bourguignat, 1852)
• Theodoxus subthermalis (Bourguignat in Issel, 1865) or Theodoxus fluviatilis subthermalis Issel, 1865
• Theodoxus transversalis
  Theodoxus transversalis
  Theodoxus transversalis is a small species of freshwater snail with an operculum. It is an aquatic gastropod mollusk in the family Neritidae, the nerites.- Distribution :Distribution of this species is Danubian.* Austria* Bulgaria* Croatia...
  
  (Pfeiffer, 1828)
• Theodoxus valentinus(Graells, 1846)

subgenus Neritaea Roth, 1855

• Theodoxus anatolicus (Récluz, 1841)
• Theodoxus jordani (Sowerby)
• Theodoxus niloticus
  Theodoxus niloticus
  Theodoxus niloticus 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 Egypt and Sudan....
  
  (Reeve, 1856) - synonym: Theodoxus africanus (Reeve, 1856)
• Theodoxus subterrelictus Schütt, 1963
• Theodoxus varius (Menke, 1828)

subgenus ?

• Theodoxus astrachanicus Starobogatov, 1994
• Theodoxus coronatus
  Theodoxus coronatus
  Theodoxus coronatus is a species of sea snail, a marine gastropod mollusk in the family Neritidae....
  
  (Leach, 1815)
• Theodoxus danasteri (Lindholm, 1908)
• Theodoxus euphraticus (Mousson, 1874)
• Theodoxus karasuna
• Theodoxus macri (Sowerby, 1849)
• Theodoxus maresi
  Theodoxus maresi
  Theodoxus maresi is a species of small freshwater snail with an operculum, an aquatic gastropod mollusk in the family Neritidae the nerites.-Distribution:...
  
  (Bourguignat, 1864)
• Theodoxus marteli (Pallary, 1920)
• Theodoxus milachevitchi Golikov & Starobogatov, 1966
• Theodoxus mutinensis
• Theodoxus numidicus
  Theodoxus numidicus
  Theodoxus numidicus is a species of small freshwater snail with an operculum, an aquatic gastropod mollusk in the family Neritidae, the nerites.-Distribution:...
  
  (Récluz, 1841)
• Theodoxus olivaceus
• Theodoxus pilidei (Tournouêr, 1879)

• Theodoxus sarmaticus (Lindholm, 1901)
• Theodoxus schultzii (Grimm, 1877)
• † Theodoxus serratiliniformis Geyer, 1914
• Theodoxus velascoi (Graëlls, 1846)

Synonyms:

• Theodoxus cariosus (Wood, 1828) and Theodoxus cariosa are synonyms of Neritina cariosa (Wood, 1828)
• Theodoxus vespertinus is a synonym of Neritina vespertinus (Sowerby, 1849)
• Theodoxus neglectus is a synonym of Neritina neglecta (Pease, 1861)

External links

• Bandel K. (2001). "The history of Theodoxus and Neritina connected with description and systematic evaluation of related Neritimorpha (Gastropoda)". Mittelungen aus dem Geologisch-Palaontologischen Institut Universitat Hamburg 85: 65-164. abstract.