扁蜷科（學名：），亦作扁卷螺科，是腹足綱之下的一個單系群支序，本科物種皆為可呼吸空氣的淡水螺。原屬有肺目基眼亞目椎實螺總科，今屬異鰓類泛有肺類喜溼螺類支序。

本科多個物種的外殼都是平旋壳（），與一般腹足綱物種的外殼形狀不同。外殼看似是右旋，但其實是螺把殼上下顛倒來揹在身上，使左旋的外殼看起來像是右旋。
因其外形，本科物種又稱。

由於本科物種的頭和腹足都比較細小，使得牠們頭上絲般幼的觸角顯得很細長。

分類
對於部份分類元來說，是否應該歸入扁蜷科仍有爭議。這對於淡水帽貝Ferrissia跟Ancylus這兩個屬來說由其合適。這些屬有時會被歸入椎实螺科（Lymnaeidae Rafinesque, 1815）；另外亦有文獻把上述兩個屬放進各自的一個科裡。然而，在布歇特和洛克羅伊的腹足類分類 (2005年)的分類，這些屬被歸為扁蜷亞科（Planorbinae）之下的Ancylini族。以下將詳述這個分類的具體內容。

2005年分類
根據布歇特和洛克羅伊的腹足類分類 (2005年)，本科包括下列各個亞科：
 扁蜷亞科 Planorbinae Rafinesque, 1815
 扁蜷族 Planorbini Rafinesque, 1815：synonyms: Choanomphalinae P. Fisher & Crosse, 1880; Orygoceratidae Brusina, 1882
 tribe Ancylini Rafinesque, 1815 - synonym: Pseudancylinae Walker, 1923 (inv.)
 tribe Biomphalariini H. Watson, 1954 - synonyms: Acrorbini Starobogatov, 1958; Drepanothrematini Zilch, 1959; Taphiinae Harry & Hubendick, 1964
 tribe Planorbulini Pilsbry, 1934
 tribe Segmentinini F.C. Baker, 1945
 subfamily Bulininae P. Fischer & Crosse, 1880
 tribe Bulinini P. Fischer & Crosse, 1880 - synonyms: Laevapicinae Hannibal, 1912; Isidorinae Annandale, 1922; Gundlachiinae Starobogatov, 1967
 tribe Coretini Gray, 1847 - synonyms: Pompholicinae Dall, 1866 (inv.); Camptoceratinae Dall, 1870; Megasystrophinae Tryon, 1871 (inv.); Pompholycodeinae Lindholm, 1927; Helisomatinae F. C. Baker, 1928; Bayardellini Starobogatov & Prozorova, 1990; Planorbariini Starobogatov, 1990
 tribe Miratestini P. & F. Sarasin, 1897 - synonyms: Ferrissiinae Walker, 1917; Ancylastrinae Walker, 1923; Protancylinae Walker, 1923; Physastrinae Starobogatov, 1958; Ameriannini Zilch, 1959; Patelloplanorbidae Franc, 1968
 tribe Plesiophysini Bequaert & Clench, 1939
 subfamily Neoplanorbinae Hannibal, 1912 - synonym: Payettiinae Dall, 1924
 subfamily Rhodacmeinae Walker, 1917

2007年本科部分物種的分類
Albrecht等(2007)分析過本科部分物種，based on sequences of mitochondrial 18S ribosomal DNA and cytochrome-c oxidase I (COI) genes, and on the basis of the results, they rearranged the taxonomy like this:

"A-clade" sensu Albrecht et al. (2007)
 Burnupia Walker, 1912

Tribus Bulinini
 Bulinus O. F. Müller, 1781
 Indoplanorbis Annandale, 1921

Tribus Ancylini Rafinesque-Schmaltz, 1815
 Ancylus O. F. Müller, 1774
 Ferrissia Walker, 1903
 Gundlachia Pfeiffer, 1849
 Laevapex Walker, 1903
 Hebetancylus Pilsbry, 1914

"B-clade" sensu Albrecht et al. (2007)
 Glyptophysa Crosse, 1872
 Protancylus Sarasin, 1897
 Kessneria Walker & Ponder 2001
 Leichhardtia Walker, 1988

Tribus Camptoceratini
 Planorbarius Duméril 1806

扁蜷族 Planorbini
 多旋螺屬 Anisus Studer, 1820
 Bathyomphalus Charpentier, 1837
 旋螺屬 Gyraulus Charpentier, 1837
 Choanomphalus Gerstfeldt, 1859
 扁蜷屬 Planorbis O. F. Müller, 1774

Tribus Segmentinini
 Segmentina 
 平扁蜷屬 Hippeutis 
 类扁蜷属 Polypylis 

"C-Clade" sensu Albrecht et al. (2007)
 Biomphalaria Preston, 1910
 Menetus H. & A. Adams, 1855
 Planorbella Haldeman, 1843
 Planorbula Haldeman, 1843

Cladogram
The following is a cladogram that shows the phylogenic relationships within the Planorbidae according to Albrecht 2007:

屬
本科的模式屬是 Planorbis 。以下列出主要根據布歇特及其他人(2005)的分類，因為Albrecht (2007)的分類並未整全的包括本科所有的屬。至於每個屬的亞屬則依照 Glöer (2002) 的文獻。以下綜合三份文獻的結果：

 扁蜷亞科 Planorbinae Rafinesque, 1815
 ?
多旋螺屬 Anisus S. Studer, 1820
 subgenus Disculifer C. Boettger, 1944
 Bathyomphalus Charpentier, 1837
 旋螺属 Gyraulus Charpentier, 1837
 subgenus Torquis Dall, 1905
 subgenus Lamorbis Starobogatov, 1967
 subgenus Armiger Hartmann, 1843
 平扁蜷屬 Hippeutis Charpentier, 1837：又名圓扁螺屬
 tribe Ancylini Rafinesque, 1815 
 Ancylus O. F. Müller, 1773 - type genus of tribe Ancylini
 tribe Biomphalariini H. Watson, 1954
 Biomphalaria Preston, 1910 - type genus of tribe Biomphalariini
 Drepanotrema Crosse & P. Fischer, 1880
 扁卷螺族 Planorbini Rafinesque, 1815
 扁卷螺屬 Planorbis Müller, 1773
 tribe Planorbulini Pilsbry, 1934
 Planorbula Haldeman, 1840 - type genus of tribe Planorbulini
 tribe Segmentinini F.C. Baker, 1945
 Segmentina Fleming, 1818 - type genus of tribe Segmentinini
淤泥螺亞科 Bulininae P. Fischer & Crosse, 1880
印度扁卷螺屬 Indoplanorbis Annandale & Prashad, 1920：單型屬，只有Indoplanorbis exustus一個物種。
 Planorbarius Duméril, 1806
 Planorbella Haldeman, 1842
 Menetus H. Adams & A. Adams, 1855
 subgenus Dilatata Clessin, 1885
 tribe Bulinini P. Fischer & Crosse, 1880
 Bulinus O. F. Müller, 1781 - type genus of subfamily Bulininae
 Gundlachia Pfeiffer, 1849
 tribe Coretini Gray, 1847 
 Coretus Gray, 1847 - type genus of tribe Coretini
 tribe Miratestini P. & F. Sarasin, 1897
 Miratesta P. & F. Sarasin, 1897 - type genus of tribe Miratestini
 Amerianna Strand, 1928
 Ferrissia Walker, 1903
 Pettancyclus Iredale, 1943
 tribe Plesiophysini Bequaert & Clench, 1939
 Plesiophysa P. Fischer, 1883 - type genus of tribe Plesiophysini
 subfamily Neoplanorbinae Hannibal, 1912
 Neoplanorbis Pilsbry, 1906 - type genus of subfamily Neoplanorbinae
 subfamily Rhodacmeinae Walker, 1917
 Rhodacmea Walker, 1917 - type genus of subfamily Rhodacmeinae

Subfamily = ? (other genera that are not yet sorted are listed here)
 Acrorbis Odhner, 1937
 Africanogyrus Özdikmen & Darilmaz, 2007 - synonym: Afrogyrus Brown & Mandahl-Barth, 1973 
 Afroplanorbis Thiele, 1931
 Amphigyra Pilsbry, 1906
 Anisopsis Sandberger, 1875
 Antillorbis Harry & Hubendick, 1964
 Armigerus Clessin, 1884
 Australorbis Pilsbry, 1934
 Bayardella Burch, 1977
 Berellaia Laubrière & Carez, 1880
 Camptoceras Benson, 1843
 Camptoceratops Wenz, 1923
 Carinifex W.G. Binney, 1865
 Carinogyraulis Polinski, 1929
 Ceratophallus Brown & Mandahl-Barth, 1973
 Choanomphalus Gerstfeldt, 1859
 Culmenella Clench, 1927
 Fossulorbis Pilsbry, 1934
 Glyptophysa Crosse, 1872
 Helicorbis Benson, 1855
 Helisoma Swainson, 1840
 Intha Annandale, 1922
 Isidorella Tate, 1896
 Kessneria Walker & Ponder, 2001
 Leichhardtia Walker, 1988
 Lentorbis Mandahl-Barth, 1954
 Macrophysa (Meek) Dall, 1870
 Paraplanorbis Hanna, 1922
 Patelloplanorbis Hubendick, 1957
 Pecosorbis D.W. Taylor, 1985
 Pentagoniostoma Branson, 1935
 Perrinilla Hannibal, 1912
 Physastra Tapparone-Canefri, 1883
 Physopsis Krauss, 1848
 Pingiella F.C. Baker, 1945
 Pitharella F. Edwards, 1860
 Planorbifex Pilsbry, 1935
 Planorbina Haldeman, 1842
 Platyphysa P. Fischer, 1883
 Platytaphius Pilsbry, 1924
 Polypylis Pilsbry, 1906
 Promenetus F.C. Baker, 1935
 Protancylus P. & F. Sarasin, 1897
 Pygmanisus Iredale, 1943
 Segmentorbis Mandahl-Barth, 1954
 Sineancylus Gutiérrez Gregoric, 2014
 Syrioplanorbis F.C. Baker, 1945
 Trochorbis Benson, 1855
 Vorticifex Meek in Dall, 1870

The genus Camptoceratops Wenz, 1923 is no longer considered to be a planorbid. It was recognised by Curry (1965, p. 360) as a euthecosomatous pteropod (Heterobranchia) (note by Arie W. Janssen, 092507).

The generic name Taphius H. Adams & A. Adams, 1855 is a synonym for Biomphalaria.

Shell description

The shells of most species in this family are disk-like or button-like, being coiled in one plane, although several groups have shells that are more higher-spired, and some are limpet-like.

All coiled shell Planorbidae are sinistral in their shell coiling, as is proved by their internal anatomy (the respiratory and the genital orifice are situated on the left side), however the animals carry their shells with what would normally be the ventral (i.e. umbilical) surface uppermost, and because of this, the shells appear to be dextral.

Indeed, formerly planorbids were thought to have dextral shells, and so species of this family were figured as if they had dextral shells. Although it is now understood that these species are sinistral in shell coiling, disk-like Planorbid shells are often still shown in illustrations oriented as if they were dextral.

Most species of coiled planorbids have a rather thin and moderately smooth shell, although more distinct sculpture such as a keel occurs in, and is diagnostic of, certain species. In the flat, keeled species, the whorls tend to overlap.

The aperture has a sharp outer lip. A peristome can be present, but often the lip is not thickened nor reflected. Those planorbid species which have a high-spired shell may have a narrow umbilicus, but frequently this is covered by callus.

In height most species vary between 6 mm and 6 cm, however, disk-like shells are usually less than about 2 cm in maximum dimension.

Like all pulmonate aquatic snails, ramshorn shells do not have an operculum to close the shell aperture.

Sinistral shells

Flat-coiled planorbid gastropod shells are hard to understand in terms of their coiling and orientation. Many of the shells of species in this family are almost planispiral in coiling such that one side of the shell often looks rather like the other side, but it is important to bear in mind that nonetheless there is an umbilical side and a spire side of the shell. In addition these are in fact sinistral shells, despite the fact that the snail carries its shell as if it were a normal dextral shell. To make sense of the shell coiling, the following facts are useful:

 In life, these pond snails hold their shells upside down compared to the normal gastropod shell orientation, with the umbilicus facing upwards
 The spire of the shell is quite sunken in many species, in addition it is carried facing downwards
 The umbilicus of the shell is very wide and shallow
 In some species the umbilicus is not as deeply "dished" as the sunken spire is, so superficially it can be hard to tell one from the other

However, once it is understood that the planorbid shell is sinistral, if the shell is held with the aperture on the left and facing the observer, then the sunken spire side of the shell is uppermost. This is a convenience for understanding the shell, but is the opposite of the way the shell is actually carried in life.

The side of the shell which is in fact the spire (a sunken spire) faces down'' in the living animal, contrary to what is the case in almost all other shelled gastropods. Because the shell is carried "upside down" like this, the aperture of the shell is angled to face downwards also, so the aperture faces a little towards the spire, not away from it, as is usually the case in other shelled gastropods.

血色素
相對於其他的軟體動物，扁卷螺科物種的血液都含有血紅素。因此，這些動物呼吸氧氣時都較其他軟體動物來得更有效；而血紅素亦令這些動物的身體帶紅色，這尤其在白化物種身上更明顯。

習性
扁卷螺科的大多數物種都只能在淡水生活，只有少數物種能存活於鹹淡水交界。所以對於其他未能存活於鹹淡水的物種，亦令農夫可以用食鹽來清除牠們。

Geological history
Ancestors of ramshorn snails are known with certainty since the Jurassic period. Modern taxa developed since the Cretaceous.

Geographical distribution
Species in this family occur worldwide. In Northwest Europe about 20 species are known (including non-indigenous species). In this region, various extinct taxa are known to have occurred, starting in the Jurassic period.

參看
膀胱螺科

參考文獻

外部連結

  NCBI Taxonomy Browser: Planorbidae 
  Systema naturae 2000 (classification) - Taxon: Planorbidae 
 
  http://mkohl1.net/Planorbidae.html 
 Frank Collins Baker, The Molluscan Family Planorbidae, The University of Illinois press, Urbana, 1945

 
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