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''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.〔Neubauer, Thomas A. (2014). ''Theodoxus'' (''Theodoxus'') ''fluviatilis'' (Linnaeus, 1758). Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=821986 on 2014-11-18〕 This widely distributed neritid snail species occurs from Europe to Central Asia. It has a thick shell with a calcified operculum. The coloration pattern on the shell is very variable. ''Theodoxus fluviatilis'' lives in freshwater and in brackish water, in rivers and lakes on stones. It feeds mainly by grazing on biofilms and diatoms. Some of the populations of this species are spreading, and these can reach densities up to thousands of snails per square meter. Females lay egg capsules, each of which contains a large number of eggs, but only one snail hatches from the capsule. The snails reach sexual maturity in a year, and the total lifespan is 2 or 3 years. ==Taxonomy== ''Theodoxus fluviatilis'' was originally described under the name ''Nerita fluviatilis'' by Carl Linnaeus in 1758. Linnaeus' original text (the type description) in Latin was very short, and reads as follows:〔 Which means in English: "''Nerita fluviatilis'', number 632: the shell is wrinkled, there are no teeth in the aperture. It inhabits rivers in Europe." Later, this species was moved to the genus ''Theodoxus'' Montfort, 1810. ''Theodoxus fluviatilis'' is in fact the type species of the genus ''Theodoxus''.〔 Anistratenko and colleagues designated the lectotype for ''Theodoxus fluviatilis'' in 1999〔 Anistratenko O. Yu., Starobogatov Ya. I. & Anistratenko V. V. (1999). "Моллюски рода ''Theodoxus'' (Gastropoda, Pectinibranchia, Neritidae) Азово-Черноморского бассейна. Molluscs of the genus ''Theodoxus'' (Gastropoda, Pectinibranchia, Neritidae) from the Black and the Azov Seas basin". ''Vestnik Zoologii'' 33(3): 11–19.〕 (an English translation was published by Anistratenko in 2005).〔Anistratenko V. V. (2005). "Lectotypes for ''Tricolia pullus'', ''Gibbula divaricata'' and ''Theodoxus fluviatilis'' (Mollusca, Gastropoda) revisited". ''Vestnik zoologii'' 39(6): 3–10. (PDF ).〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Theodoxus fluviatilis」の詳細全文を読む スポンサード リンク
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