Planorbidae

Planorbidae, common name the ramshorn snails or ram's horn snails, is a family of air-breathing freshwater snails, aquatic pulmonate gastropod molluscs. Unlike most molluscs, the blood of ram's horn snails contains iron-based hemoglobin instead of copper-based hemocyanin. As a result, planorbids are able to breathe oxygen more efficiently than other molluscs. The presence of hemoglobin gives the body a reddish colour. This is especially apparent in albino animals.
Being air breathers like other Panpulmonata, planorbids do not have gills, but instead, have a lung. The foot and head of planorbids are rather small, while their thread-like tentacles are relatively long. Many of the species in this family have coiled shells that are planispiral, in other words, the shells are more or less coiled flat, rather than having an elevated spire as is the case in most gastropod shells. Although they carry their shell in a way that makes it appear to be dextral, the shell of coiled planorbids is in fact sinistral in coiling, but is carried upside down, which makes it appear to be dextral.
General taxonomic context
For several taxa, no consensus exists as to whether the taxa should even be assigned to the family Planorbidae. This is certainly the case with the freshwater limpets Ferrissia, and Ancylus. Both of these genera have sometimes been assigned to the family Lymnaeidae. Alternatively, sometimes each one of them is raised to the level of a family. However, according to the taxonomy of the Gastropoda (Bouchet & Rocroi, 2005), these genera are currently placed in the tribe Ancylini within the family Planorbidae, and that is the taxonomic system that is followed here.
2005 taxonomy
According to the taxonomy of the Gastropoda (Bouchet & Rocroi, 2005), this family consists of the following subfamilies:
subfamily Planorbinae Rafinesque, 1815
tribe Planorbini Rafinesque, 1815 - synonyms: Choanomphalinae Fisher & Crosse, 1880; Orygoceratidae Brusina, 1882
tribe Ancylini Rafinesque, 1815 - synonym: Pseudancylinae Walker, 1923 (inv.)
tribe Biomphalariini Watson, 1954 - synonyms: Acrorbini Starobogatov, 1958; Drepanothrematini Zilch, 1959; Taphiinae Harry & Hubendick, 1964
tribe Planorbulini Pilsbry, 1934
tribe Segmentinini Baker, 1945
subfamily Bulininae Fischer & Crosse, 1880
tribe Bulinini 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 Baker, 1928; Bayardellini Starobogatov & Prozorova, 1990; Planorbariini Starobogatov, 1990
tribe Miratestini Sararsin & 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 taxonomy for part of the family
Albrecht et al. (2007) analyzed a limited number of genera of Planorbidae, 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 Müller, 1781
Indoplanorbis Annandale, 1921
Tribus Ancylini Rafinesque-Schmaltz, 1815
Ancylus 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
Tribus Planorbini
Anisus Studer, 1820
Bathyomphalus Charpentier, 1837
Gyraulus Charpentier, 1837
Hovorbis Brown & Mandahl-Barth, 1973
Choanomphalus Gerstfeldt, 1859
Planorbis Müller, 1774
Tribus Segmentinini
Segmentina Fleming, 1818
Hippeutis Charpentier, 1837
Polypylis Pilsbry, 1906
"C-Clade" sensu Albrecht et al., (2007)
Biomphalaria Preston, 1910
Menetus Adams & 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:
Genera
The type genus of this family is Planorbis Müller. The following list of genera is organized according to the 2005 taxonomy, because Albrecht's 2007 taxonomy is not available for all genera of Planorbidae.
Genera in the family Planorbidae include (subgenera listed according to Glöer (2002):
subfamily Planorbinae Rafinesque, 1815
Anisus S. Studer, 1820
subgenus Disculifer Boettger, 1944
Bathyomphalus Charpentier, 1837
Gyraulus Charpentier, 1837
subgenus Torquis Dall, 1905
subgenus Lamorbis Starobogatov, 1967
subgenus Armiger Hartmann, 1843
Hippeutis Charpentier, 1837
tribe Ancylini Rafinesque, 1815
Ancylus Müller, 1773 - type genus of tribe Ancylini
tribe Biomphalariini Watson, 1954
Biomphalaria Preston, 1910 - type genus of tribe Biomphalariini
Drepanotrema Crosse & Fischer, 1880
tribe Planorbini Rafinesque, 1815
Afrogyrorbis Starobogatov, 1967
Planorbis Müller, 1773
tribe Planorbulini Pilsbry, 1934
Planorbula Haldeman, 1840 - type genus of tribe Planorbulini
tribe Segmentinini Baker, 1945
Segmentina Fleming, 1818 - type genus of tribe Segmentinini
subfamily Bulininae Fischer & Crosse, 1880
Indoplanorbis Annandale & Prashad, 1920 - contains one species Indoplanorbis exustus
Planorbarius Duméril, 1806
Planorbella Haldeman, 1842
Menetus Adams & Adams, 1855
subgenus Dilatata Clessin, 1885
tribe Bulinini Fischer & Crosse, 1880
Bulinus Müller, 1781 - type genus of subfamily Bulininae
Gundlachia Pfeiffer, 1849
tribe Coretini Gray, 1847
Coretus Gray, 1847 - type genus of tribe Coretini
tribe Miratestini Sarasin & Sarasin, 1897
Miratesta Sarasin & Sarasin, 1897 - type genus of tribe Miratestini
Amerianna Strand, 1928
Ferrissia Walker, 1903
Pettancyclus Iredale, 1943
tribe Plesiophysini Bequaert & Clench, 1939
Plesiophysa 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 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 Taylor, 1985
Pentagoniostoma Branson, 1935
Perrinilla Hannibal, 1912
Physastra Tapparone-Canefri, 1883
Physopsis Krauss, 1848
Pingiella Baker, 1945
Pitharella Edwards, 1860
Planorbifex Pilsbry, 1935
Planorbina Haldeman, 1842
Platyphysa Fischer, 1883
Platytaphius Pilsbry, 1924
Polypylis Pilsbry, 1906
Promenetus Baker, 1935
Protancylus Sarasin & Sarasin, 1897
Pygmanisus Iredale, 1943
Segmentorbis Mandahl-Barth, 1954
Sineancylus Gutiérrez Gregoric, 2014
Syrioplanorbis 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 Adams & 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.
Habitat
Most species of planorbids live only in fresh water, such as ponds, lakes, and slow moving rivers. A minority of species are able to survive in brackish water.
Geological history
Ancestors of ramshorn snails are known with certainty since the Jurassic period. Modern taxa developed in the Jurassic.
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.
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, & 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.
External links
NCBI Taxonomy Browser: Planorbidae
Systema naturae 2000 (classification) - Taxon: Planorbidae
ITIS: Planorbidae
http://mkohl1.net/Planorbidae.html
Frank Collins Baker, The Molluscan Family Planorbidae, The University of Illinois press, Urbana, 1945
Gastropod families
Taxa named by Constantine Samuel Rafinesque