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Planorbidae

(Family)

Overview

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Planorbidae, common name the ramshorn snails or ram's horn snails, is a family of air-breathing freshwater snails, aquatic pulmonate gastropod mollusks.

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.

Their foot and head are rather small, while their thread-like tentacles are relatively long.

For what are known as "ramshorn snails" in the aquarium trade, some of which but not all of which are planorbids, please see ramshorn snail.

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For several taxa, no consensus exists as to whether the taxa should even be assigned to the family Planorbidae. This is certainly the case wi th 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. 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:

2007 taxonomy

A cladogram based on sequences of mitochondrial 18S ribosomal DNA and cytochrome-c oxidase I (COI) genes showing phylogenic relations of Planorbidae:[3]

Albrecht et al. (2007)[3] have analyzed a limited number of genera of Planorbidae and rearranged taxonomy like this:

"A-clade" sensu Albrecht et al. (2007)[3]

Tribus Bulinini

Tribus Ancylini Rafinesque-Schmaltz, 1815

"B-clade" sensu Albrecht et al. (2007)[3]

Tribus Camptoceratini

Tribus Planorbini

Tribus Segmentinini

"C-Clade" sensu Albrecht et al. (2007)[3]

Genera

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Planorbis M?ller, 1773 is the type genus of this family.

Genera in the family Planorbidae include (subgenera according to Gl?er (2002)[4]). Organized per 2005 taxonomy, because Albrecht's 2007 taxonomy is not available for all genera of Planorbidae.

View of the sunken spire of the shell of A nisus septemgyratus

subfamily ? (other genera not yet sorted here)

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).

Taphius H. Adams & A. Adams, 1855 is a synonym for Biomphalaria.[5]

Shell description

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Apical, apertural and umbilical view of the shell of Biomphalaria tenagophila. Scale bar is 3 mm.

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 still figured as if they were dextral (in other words in illustrations in standard texts, the shells are still oriented as if they were dextral, for comparative purposes.)

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. And in tis flat, keeled specimens, the whorls tend to ove rlap.

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

Planorbarius corneus. View of the sunken spire (held facing downwards in life)
Planorbarius corneus. View of the umbilicus (held uppermost in life)

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:

Note that in life the shell is held so that the aperture is on the right, which makes the shell appear to be dextral

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 actua lly 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.

Blood pigment

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

Habitat

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Most species of planorbids live only in fresh water. A minority of species are able to survive in brackish w ater.

Geological history

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

Geographical distribution

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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.

esque-Schmaltz, 1815

"B-clade" sensu Albrecht et al. (2007)[3]

Tribus Camptoceratini

Tribus Planorbini

Tribus Segmentinini

"C-Clade" sensu Albrecht et al. (2007)[3]

Genera

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Planorbis M?ll er, 1773 is the type genus of this family.

Genera in the family Planorbidae include (subgenera according to Gl?er (2002)[4]). Organized per 2005 taxonomy, because Albrecht's 2007 taxonomy is not available for all genera of Planorbidae.

View of the sunken spire of the shell of Anisus septemgyratus

subfamily ? (other genera not yet sorted here)

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).

Taphius H. Adams & A. Adams, 1855 is a synonym for Biomphalaria.[5]

Shell description

[ Back to top ]
Apical, apertural and umbilical view of the shell of Biomphalaria tenagophila. Scale bar is 3 mm.

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 ap pear 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 still figured as if they were dextral (in other words in illustrations in standard texts, the shells are still oriented as if they were dextral, for comparative purposes.)

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. And in tis flat, keeled specimens, 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

Planorbarius corneus. View of the sunken spire (held facing downwards in life)
Planorbarius corneus. View of the umbilicus (held uppermost in life)

Flat-coiled planorbid gastropod shells are h ard 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:

Note that in life the shell is held so that the aperture is on the right, which makes the shell appear to be dextral

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.

Blood pigment

[ Back to top ]

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

Habitat

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Most species of planorbids live only in fresh water. A minority of species are able to survive in brackish water.

Geological history

[ Back to top ]

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

Geographical distribution

[ Back to top ]

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

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  1. ^ Rafinesque C. S. 1815. Analyse de la Nature ou tableau de l'univers et des corps organis?s. Palermo, 223 pp., page 143.
  2. ^ Strong E. E., Gargominy O., Ponder W. F. & Bouchet P. (2008). "Global Diversity of Gastropods (Gastropoda; Mollusca) in Freshwater". Hydrobiologia 595: 149-166. http://hdl.handle.net/10088/7390 doi:10.1007/s10750-007-9012-6.
  3. ^ a b c d e Albrecht C., Kuhn K. & Streit B. (2007). "A molecular phylogeny of Planorboidea (Gastropoda, Pulmonata): insights from enhanced taxon sampling". Zoologica Scripta 36: 27-39. doi:10.1111/j.1463-6409.2006.00258.x.
  4. ^ (German) Gl?er P. 2002. Die S??wassergastropoden Nord- und Mitteleuropas. Die Tierwelt Deutschlands, ConchBooks, Hackenheim, 326 pp., ISBN 3-925919-60-0, page 19-20.
  5. ^ a b c d e f g h i j k l m Bouchet P., Rocroi J.-P., Fr?da J., Hausdorf B., Ponder W., Vald?s ?. & War?n A. (2005 ). "Classification and nomenclator of gastropod families". Malacologia: International Journal of Malacology (Hackenheim, Germany: ConchBooks) 47 (1-2): 1?397. ISBN 3925919724. ISSN 0076-2997. http://www.archive.org/details/malacologia47122005inst. 
  6. ^ Liu L et al. (2010) "The phylogeography of Indoplanorbis exustus (Gastropoda: Planorbidae) in Asia". Parasites & Vectors 3: 57. doi:10.1186/1756-3305-3-57.
  7. ^ Mollusc Specialist Group (1996). Culmenella rezvoji. In: IUCN 2010. IUCN Red List of Threatened Species. Version 2010.4. <www.iucnredlist.org>. Downloaded on 08 March 2011.

External links

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Taxonomy

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The Family Planorbidae is a member of the Superfamily Planorboidea. Here is the complete "parentage" of Planorbidae:

The Family Planorbidae is further organized into finer groupings including:

Genera

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Aenigmomphisicola

[more]

Africanogyrus

[more]

Afrogyrus

Africanogyrus is a genus of air-breathing freshwater snail, an aquatic pulmonate gastropod mollusk in the family Planorbidae, the ram's horn snails and their allies. [more]

Ameria

Amelia is a town and comune of the province of Terni, in the Umbria region of central Italy. It grew up around an ancient hill fort, known to the Romans as . [more]

Amerianna

[more]

Ancylastrum

Ancylastrum is a genus of air-breathing freshwater limpets, aquatic pulmonate gastropod mollusks in the family Planorbidae, the ram's horn snails and their allies. [more]

Ancylus

Ancylus is a genus of very small, freshwater, air-breathing limpets. They are aquatic pulmonate gastropod mollusks in the tribe Ancylini within the family Planorbidae, the ram's horn snails and their allies. [more]

Anisancylus

[more]

Anisus

Anisus is a genus of small air-breathing freshwater snails, aquatic pulmonate gastropod mollusks in the family Planorbidae, the ramshorn snails and their allies. [more]

Armiger

In heraldry, an armiger is a person entitled to use a coat of arms. Such a person is said to be armigerous. [more]

Australorbis

[more]

Bathyomphalus

[more]

Bayardella

[more]

Biomphalaria

Biomphalaria is a genus of air-breathing freshwater snails, aquatic pulmonate gastropod mollusks in the family Planorbidae, the ram's horn snails and their allies. [more]

Camptoceras

Camptoceras is a genus of in the Planorbidae family. It contains the following species: [more]

Carinifex

[more]

Ceratophallus

Ceratophallus is a genus of snails in the Planorbidae family. They are found in Africa and some Indian Ocean islands. The genus contains the following species: [more]

Choanomphalus

[more]

Culmenella

Drepanotrema

[more]

Glyptophysa

Glyptophysa is a genus of in the Planorbidae family. It contains the following species: [more]

Gyraulus

Gyraulus is a genus of small, mostly air-breathing, freshwater snails, aquatic pulmonate gastropod mollusks in the family Planorbidae, the ram's horn snails. [more]

Helicorbis

Helisoma

[more]

Hippeutis

[more]

Kolhymorbis

Leichhardtia

Leichhardtia is a genus of air-breathing freshwater snails, aquatic pulmonate gastropod mollusks in the family Planorbidae, the ram's horn snails. [more]

Lentorbis

[more]

Menetus

[more]

Micromenetus

Miratesta

Miratesta is a genus of in the Planorbidae family. It contains the following species: [more]

Parapholyx

Pecosorbis

[more]

Physastra

[more]

Physopsis

[more]

Planorbarius

[more]

Planorbella

Planorbella is a genus of freshwater air-breathing snails, aquatic pulmonate gastropod mollusks in the family Planorbidae, the ram's horn snails, or planorbids, which all have sinistral, or left-coiling, shells. [more]

Planorbis

Planorbis is a genus of freshwater air-breathing snails, aquatic pulmonate gastropod mollusks in the family Planorbidae, the ram's horn snails, or planorbids. All species in this genus have sinistral or left-coiling shells. [more]

Planorbula

[more]

Polypylis

Promenetus

[more]

Segmentina

[more]

Segmentorbis

Simulator

A Genus in the Kingdom Animalia. [more]

Spiralina

Trochorbis

Tropicorbis

[more]

Uncancylus

Vorticifex

[more]

At least 10 species and subspecies belong to the Genus Vorticifex.

More info about the Genus Vorticifex may be found here.

References

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  1. ^ Rafinesque C. S. 1815. Analyse de la Nature ou tableau de l'univers et des corps organis?s. Palermo, 223 pp., page 143.
  2. ^ Strong E. E., Gargominy O., Ponder W. F. & Bouchet P. (2008). "Global Diversity of Gastropods (Gastropoda; Mollusca) in Freshwater". Hydrobiologia 595: 149-166. http://hdl.handle.net/10088/7390 doi:10.1007/s10750-007-9012-6.
  3. ^ a b c d e Albrecht C., Kuhn K. & Streit B. (2007). "A molecular phylogeny of Planorboidea (Gastropoda, Pulmonata): insights from enhanced taxon sampling". Zoologica Scripta 36: 27-39. doi:10.1111/j.1463-6409.2006.00258.x.
  4. ^ (German) Gl?er P. 2002. Die S??wassergastropoden Nord- und Mitteleuropas. Die Tierwelt Deutschlands, ConchBooks, Hackenheim, 326 pp., ISBN 3-925919-60-0, page 19-20.
  5. ^ a b c d e f g h i j k l m Bouchet P., Rocroi J.-P., Fr?da J., Hausdorf B., Ponder W., Vald?s ?. & War?n A. (2005). "Classification and nomenclator of gastropod families". Malacologia: International Journal of Malacology (Hackenheim, Germany: ConchBooks) 47 (1-2): 1?397. ISBN 3925919724. ISSN 0076-2997. http://www.archive.org/details/malacologia47122005inst. 
  6. ^ Liu L et al. (2010) "The phylogeography of Indoplanorbis exustus (Gastropoda: Planorbidae) in Asia". Parasites & Vectors 3: 57. doi:10.1186/1756-3305-3-57.
  7. ^ Mollusc Specialist Group (1996). Culmenella rezvoji. In: IUCN 2010. IUCN Red List of Threatened Species. Version 2010.4. <www.iucnredlist.org>. Downloaded on 08 March 2011.

Sources

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Last Revised: August 24, 2012
2012/08/24 13:39:56