Planorbidae, or ram's-horn shells, is a family of freshwater gastropods.

Type genus

Planorbis Müller, 1773 is the type genus of this family.

Taxonomy and systematics

Much confusion has existed about the hierarchy and the position of the mentioned planorbid genera. Several taxa that are considered to be a genus on this page are considered elsewhere to be a subgenus, whereas the reverse may also occur. For several taxa even no consensus exists for the assignment to the Planorbidae family. This is for instance the case with Ferrissia and Ancylus. Both may also be found assigned to the Lymnaeidae family or even raised to family level each. Regarding the taxonomy, systematics, and nomenclature of the Planorbidae for Europe the work of CLECOM should be decisive. If CLECOM isn't helpful, other sources come into consideration. Although reference can be made to taxonomical databases on the internet (NCBI and Taxonomicon) it should be emphasized that these are incomplete and contain errors (also in the present family) that becomes apparent when the same taxon appears in various genera.

According to the new Taxonomy of the Gastropoda (Bouchet & Rocroi, 2005) this family consists of the following subfamiliers :

• subfamily Bulininae P. Fischer & Crosse, 1880
• tribe Bulinini P. Fischer & Crosse, 1880
• tribe Coretini Gray, 1847
• tribe Miratestini P.1F. Sarasin, 1897
• tribe Plesiophysini Bequaert & Clench, 1939
• subfamily Neoplanorbinae Hannibal, 1912
• subfamily Planorbinae Rafinesque, 1815
• tribe Ancylini Rafinesque, 1815
• tribe Biomphalaeiini H. Watson, 1954
• tribe Planorbini Rafinesque, 1815
• tribe Planorbulini Pilsbry, 1934
• tribe Segmentinini F.C. Baker, 1945
• subfamily Rhodacmeinae Walker, 1917

Genera

Acrorbis Odhner, 1937 Afrogyrus Brown & Mandahl-Barth, 1973 Afroplanorbis Thiele, 1931 Amerianna Strand, 1928 Amphigyra Pilsbry, 1906 Anisopsis Sandberger, 1875 Anisus S. Studer, 1820 Antillorbis Harry & Hubendick, 1964 Armigerus Clessin, 1884 Australorbis Pilsbry, 1934 Bathyomphalus Charpentier, 1837 Bayardella Burch, 1977 Berellaia Laubrière & Carez, 1880 Biomphalaria Preston, 1910 Bulinus Müller, 1774 Camptoceras Benson, 1843 Camptoceratops Wenz, 1923 Carinifex W.G. Binney, 1865 Carinogyraulis Polinski, 1929 Ceratophallus Cope, 1893 Choanomphalus Gerstfeldt, 1859 Drepanotrema Crosse & Fischer, 1880

Ferrissia Walker, 1903 Fossulorbis Pilsbry, 1934 Glyptophysa Crosse, 1872 Gyraulus Charpentier, 1837 Helicorbis Benson, 1855 Helisoma Swainson, 1840 Hippeutis Charpentier, 1837 Indoplanorbis Annandale & Prashad, 1920 Intha Annandale, 1922 Isidorella Tate, 1896 Kessneria Walker & Ponder, 2001 Leichhardtia Walker, 1988 Lentorbis Mandahl-Barth, 1994 Macrophysa (Meek) Dall, 1870 Menetus H. & A. Adams, 1855 Miratesta P. & F. Sarasin, 1897 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 Planorbarius Duméril, 1806 Planorbella Haldeman, 1842 Planorbifex Pilsbry, 1935 Planorbina Haldeman, 1842 Planorbis Müller, 1773 Planorbula Haldeman, 1840 Platyphysa P. Fischer, 1883 Platytaphius Pilsbry, 1924 Plesiophysa P. Fischer, 1883 Polypylis Pilsbry, 1906 Promenetus F.C. Baker, 1935 Protancylus P. & F. Sarasin, 1897 Pygmanisus Iredale, 1943 Segmentina Fleming, 1817 Segmentorbis Mandahl-Barth, 1954 Syrioplanorbis F.C. Baker, 1945 Taphius H. & A. Adams, 1855 Trochorbis Benson, 1855 Vorticifex Meek in Dall, 1870

The genus Camptoceratops Wenz, 1923 is not a planorbid. It was recognised by Curry (1965, p. 360) as a euthecosomatous pteropod (Heterobranchia) (note by Arie W. Janssen, 092507)

Shell characters

The shells of most species show a disk-like shell that is coiled in one plane. Several groups are higher spired and these are sinistral. As a matter of fact all Planorbidae are sinistral. This is shown by their anatomy. Formerly this was not known and species of this family, therefore, have often been figured with 'dextral' shells. Nowadays the rule still is to figure disk-like Planorbidae in this way. Most species have a rather thin and moderately smooth shell, although more distinct sculptures such as keels occur as well.

The aperture has a sharp outer lip. A peristome can be present but often the lip is not thickened nor reflected. Species possessing a high spired shell may have a narrow umbilicus but mostly this is covered by callus.

In height most species vary between 6 mm and 6 cm, however, disk-like shells mostly remain less than about 2 cm.

Ramshorn shells do not have an operculum to close their aperture.

Animal

Contrary to most other molluscs the blood of ram's-horn snails contains hemoglobine. As a result these animals are able to breath oxygen more efficiently than other molluscs. The presence of this substance gives the body a reddish colour. This is especially apparent in albino animals.

Habitat

Most species thrive in fresh water, and a minority of the species are able to survive in brackish water.

Geological history

Ancestors of ram's-horn snails are known with certainty since the Jurassic era. Modern taxa developed since the Cretaceous.

Geographical distribution

Worldwide.

Occurrence in Northwest Europe

In Northwest Europe about 20 species are known (including non-indigenous species). In this region extinct taxa are known as well since the Jurassic.

External links

• CLECOM (Check List of European COntinental Mollusca)
• NCBI Taxonomy Browser: Planorbidae
• Systema naturae 2000 (classification) - Taxon: Planorbidae
• ITIS: Planorbidae
• http://members.aol.com/mkohl2/Planorbidae.html

References

• Gittenberger, E., Janssen, A.W., Kuijper, W.J., Kuiper, J.G.J., Meijer, T., Velde, G. van der & Vries, J.N. de (1998) De Nederlandse zoetwatermollusken. Recente en fossiele weekdieren uit zoet en brak water Nederlandse Fauna 2. Nationaal Natuurhistorisch Museum Naturalis, KNNV Uitgeverij & EIS-Nederland, Leiden, 288 pp.
• Fischer, P.H. (1880-1887) Manuel de Conchyliologie et de Paléontologie conchyliologique ou histoire naturelle des Mollusques vivants et fossiles suivi d'un appendice sur les Brachiopodes par D. Oehlert. – XXIV + 1369 pp.
• (German) Thiele, J. (1929-1935) Handbuch der Systematischen Weichtierkunde. Jena, (1), 1-376, 1929; (2), 377-778, 1931; 779-1022, 1934; 1023-1134, 1935.
• Vaught, K.C. (1989) A classification of living mollusca. American Malacologists Inc., Melbourne USA, ISBN 0-915826-22-4 & 0-915826-22-6, 195 pp.
• (German) Wenz, W. (1923-1930) Gastropoda extramarina tertiaria. Fossilium Catalogus I. (4 vols.), 3387 pp.
• (German) Zilch, A. (1959-1960) Euthyneura. In: H. Schindewolf (ed.), Handbuch der Paläozoologie, 6(2): pp. I-XII + 1-834.