Planorbidae
Encyclopedia
Planorbidae, common name
the ramshorn snails or ram's horn snails, is a family
of air-breathing freshwater snail
s, 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 shell
s. 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
.
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. That is the taxonomic system that is followed here.
, this family consists of the following subfamilies:
based on sequences of mitochondrial 18S ribosomal DNA and cytochrome-c oxidase I
(COI) genes showing phylogenic relations of Planorbidae:
Albrecht et al. (2007) have analyzed a limited number of genera of Planorbidae and rearranged taxonomy like this:
"A-clade" sensu Albrecht et al. (2007)
Tribus Bulinini
Tribus Ancylini Rafinesque-Schmaltz, 1815
"B-clade" sensu Albrecht et al. (2007)
Tribus Camptoceratini
Tribus Planorbini
Tribus Segmentinini
"C-Clade" sensu Albrecht et al. (2007)
, 1773 is the type genus
of this family.
Genera in the family Planorbidae include (subgenera according to Glöer (2002)). Organized per 2005 taxonomy, because Albrecht's 2007 taxonomy is not available for all genera of Planorbidae.
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
.
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 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.
Flat-coiled planorbid gastropod shell
s 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:
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.
.
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 colour. This is especially apparent in albino animals.
period. Modern taxa developed since the Cretaceous
.
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.
Common name
A common name of a taxon or organism is a name in general use within a community; it is often contrasted with the scientific name for the same organism...
the ramshorn snails or ram's horn snails, is a family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
of air-breathing freshwater snail
Freshwater snail
A freshwater snail is one kind of freshwater mollusc, the other kind being freshwater clams and mussels, i.e. freshwater bivalves. Specifically a freshwater snail is a gastropod that lives in a watery non-marine habitat. The majority of freshwater gastropods have a shell, with very few exceptions....
s, aquatic
Aquatic animal
An aquatic animal is an animal, either vertebrate or invertebrate, which lives in water for most or all of its life. It may breathe air or extract its oxygen from that dissolved in water through specialised organs called gills, or directly through its skin. Natural environments and the animals that...
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
Spire (mollusc)
A spire is a descriptive term for part of the coiled shell of mollusks. The word is a convenient aid in describing shells, but it does not refer to a very precise part of shell anatomy: the spire consists of all of the whorls except for the body whorl...
as is the case in most gastropod shell
Gastropod shell
The gastropod shell is a shell which is part of the body of a gastropod or snail, one kind of mollusc. The gastropod shell is an external skeleton or exoskeleton, which serves not only for muscle attachment, but also for protection from predators and from mechanical damage...
s. 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
Ramshorn snail
The term ramshorn snail is used in two different ways. In the aquarium trade it is used to describe various kinds of freshwater snails whose shells are planispiral, meaning that the shell is a flat coil. Such shells resemble a coil of rope, or a ram's horn...
.
Taxonomy
For several taxa, no consensus exists as to whether the taxa should even be assigned to the familyFamily (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Planorbidae. This is certainly the case with the freshwater limpets Ferrissia
Ferrissia
Ferrissia is a genus of air-breathing freshwater snail, a small freshwater limpet, an aquatic gastropod mollusk in the family Planorbidae, the ram's horn snails and their allies.-Species:Species within the genus Ferrissia include:...
, and Ancylus
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....
. Both of these genera have sometimes been assigned to the family Lymnaeidae
Lymnaeidae
Lymnaeidae is a taxonomic family of small to large air-breathing freshwater snails, aquatic pulmonate gastropod mollusks, that belong to the clade Hygrophila....
. 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)
Taxonomy of the Gastropoda (Bouchet & Rocroi, 2005)
The taxonomy of the Gastropoda as it was revised by Philippe Bouchet and Jean-Pierre Rocroi is currently the most up-to-date overall system for classifying gastropod mollusks...
, 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)Taxonomy of the Gastropoda (Bouchet & Rocroi, 2005)
The taxonomy of the Gastropoda as it was revised by Philippe Bouchet and Jean-Pierre Rocroi is currently the most up-to-date overall system for classifying gastropod mollusks...
, this family consists of the following subfamilies:
- subfamily Planorbinae Rafinesque, 1815
- tribe 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 taxonomy
A cladogramCladogram
A cladogram is a diagram used in cladistics which shows ancestral relations between organisms, to represent the evolutionary tree of life. Although traditionally such cladograms were generated largely on the basis of morphological characters, DNA and RNA sequencing data and computational...
based on sequences of mitochondrial 18S ribosomal DNA and cytochrome-c oxidase I
Main subunit of cytochrome c oxidase
Cytochrome C and Quinol oxidase polypeptide I is main subunit of cytochrome c oxidase complex.Cytochrome c oxidase is a key enzyme in aerobic metabolism. Proton pumping heme-copper oxidases represent the terminal, energy-transfer enzymes of respiratory chains in prokaryotes and eukaryotes...
(COI) genes showing phylogenic relations of Planorbidae:
Albrecht et al. (2007) have analyzed a limited number of genera of Planorbidae and rearranged taxonomy like this:
"A-clade" sensu Albrecht et al. (2007)
- BurnupiaBurnupiaBurnupia is a genus of small freshwater snails or limpets, aquatic gastropod mollusks that are traditionally placed in the family Planorbidae....
Walker, 1912
Tribus Bulinini
- BulinusBulinusBulinus is a genus of small tropical freshwater snails, aquatic gastropod mollusks in the family Planorbidae, the ramshorn snails and their allies....
O. F. Müller, 1781 - Indoplanorbis Annandale, 1921
Tribus Ancylini Rafinesque-Schmaltz, 1815
- AncylusAncylusAncylus 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....
O. F. Müller, 1774 - FerrissiaFerrissiaFerrissia is a genus of air-breathing freshwater snail, a small freshwater limpet, an aquatic gastropod mollusk in the family Planorbidae, the ram's horn snails and their allies.-Species:Species within the genus Ferrissia include:...
Walker, 1903 - GundlachiaGundlachiaGundlachia is a genus of minute freshwater snails or limpets, aquatic pulmonate gastropod mollusks in the family Planorbidae, the ram's horn snails and their allies....
Pfeiffer, 1849 - Laevapex Walker, 1903
- Hebetancylus Pilsbry, 1914
"B-clade" sensu Albrecht et al. (2007)
- GlyptophysaGlyptophysaGlyptophysa is a genus of small, left-handed or sinistral, air-breathing freshwater snails, aquatic pulmonate gastropod mollusks in the family Planorbidae.-Species:Species in the genus Glyptophysa include:* Glyptophysa petiti Crosse, 1872...
Crosse, 1872 - Protancylus Sarasin, 1897
- KessneriaKessneriaKessneria is a genus of air-breathing freshwater snails, aquatic pulmonate gastropod mollusks in the family Planorbidae, the ram's horn snails.All species within family Planorbidae have sinistral shells.-Species:Species within this genus include:...
Walker & Ponder 2001 - LeichhardtiaLeichhardtiaLeichhardtia is a genus of air-breathing freshwater snails, aquatic pulmonate gastropod mollusks in the family Planorbidae, the ram's horn snails.All species within this genus and this family have sinistral shells....
Walker, 1988
Tribus Camptoceratini
- PlanorbariusPlanorbariusPlanorbarius 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.-Species:...
Duméril 1806
Tribus Planorbini
- AnisusAnisusAnisus is a genus of small air-breathing freshwater snails, aquatic pulmonate gastropod mollusks in the family Planorbidae, the ramshorn snails and their allies.-Species:The genus contains the following species:subgenus Anisus...
Studer, 1820 - BathyomphalusBathyomphalusBathyomphalus is a genus of small air-breathing freshwater snails, aquatic pulmonate gastropod mollusks in the family Planorbidae, the ramshorn snails and their allies.-Species:Species within this genus include:...
Charpentier, 1837 - GyraulusGyraulusGyraulus is a genus of small, mostly air-breathing, freshwater snails, aquatic pulmonate gastropod mollusks in the family Planorbidae, the ram's horn snails....
Charpentier, 1837 - Choanomphalus Gerstfeldt, 1859
- PlanorbisPlanorbisPlanorbis 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.- Description :...
O. F. Müller 1774
Tribus Segmentinini
- SegmentinaSegmentinaSegmentina is a genus of small, air-breathing, freshwater snails, aquatic gastropod mollusks or micromollusks in the family Planorbidae, the ramshorn snails....
Fleming, 1818 - HippeutisHippeutisHippeutis is a genus of minute air-breathing freshwater snails, aquatic pulmonate gastropod mollusks or micromollusks in the family Planorbidae, the ramshorn snails.Albrecht et al...
Charpentier, 1837 - Polypylis Pilsbry, 1906
"C-Clade" sensu Albrecht et al. (2007)
- BiomphalariaBiomphalariaBiomphalaria is a genus of air-breathing freshwater snails, aquatic pulmonate gastropod mollusks in the family Planorbidae, the ram's horn snails and their allies.Biomphalaria is the type genus of the tribe Biomphalariini....
Preston, 1910 - MenetusMenetusMenetus is a North American genus of freshwater snails, aquatic pulmonate gastropod mollusks in the family Planorbidae, the ramshorn snails.-Species:Species within this genus include:subgenus Micromenetus F. C...
H. & A. Adams, 1855 - PlanorbellaPlanorbellaPlanorbella 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.-Understanding the shell coiling:...
Haldeman, 1843 - Planorbula Haldeman, 1843
Genera
Planorbis MüllerOtto Friedrich Müller
Otto Friedrich Müller, also Mueller was a Danish naturalist.-Biography:Müller was born in Copenhagen. He was educated for the church, became tutor to a young nobleman, and after several years' travel with him settled in Copenhagen in 1767, and married a lady of wealth.His first important works,...
, 1773 is the type genus
Type genus
In biological classification, a type genus is a representative genus, as with regard to a biological family. The term and concept is used much more often and much more formally in zoology than it is in botany, and the definition is dependent on the nomenclatural Code that applies:* In zoological...
of this family.
Genera in the family Planorbidae include (subgenera according to Glöer (2002)). Organized per 2005 taxonomy, because Albrecht's 2007 taxonomy is not available for all genera of Planorbidae.
- subfamily Planorbinae Rafinesque, 1815
-
-
- AnisusAnisusAnisus is a genus of small air-breathing freshwater snails, aquatic pulmonate gastropod mollusks in the family Planorbidae, the ramshorn snails and their allies.-Species:The genus contains the following species:subgenus Anisus...
S. Studer, 1820- subgenus Disculifer C. Boettger, 1944
- BathyomphalusBathyomphalusBathyomphalus is a genus of small air-breathing freshwater snails, aquatic pulmonate gastropod mollusks in the family Planorbidae, the ramshorn snails and their allies.-Species:Species within this genus include:...
Charpentier, 1837 - GyraulusGyraulusGyraulus is a genus of small, mostly air-breathing, freshwater snails, aquatic pulmonate gastropod mollusks in the family Planorbidae, the ram's horn snails....
Charpentier, 1837- subgenus Torquis Dall, 1905
- subgenus Lamorbis Starobogatov, 1967
- subgenus Armiger Hartmann, 1843
- HippeutisHippeutisHippeutis is a genus of minute air-breathing freshwater snails, aquatic pulmonate gastropod mollusks or micromollusks in the family Planorbidae, the ramshorn snails.Albrecht et al...
Charpentier, 1837
- Anisus
-
-
- tribe Ancylini Rafinesque, 1815
- AncylusAncylusAncylus 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....
O. F. Müller, 1773 - type genus of tribe Ancylini
- Ancylus
- tribe Biomphalariini H. Watson, 1954
- BiomphalariaBiomphalariaBiomphalaria is a genus of air-breathing freshwater snails, aquatic pulmonate gastropod mollusks in the family Planorbidae, the ram's horn snails and their allies.Biomphalaria is the type genus of the tribe Biomphalariini....
Preston, 1910 - type genus of tribe Biomphalariini - Drepanotrema Crosse & P. Fischer, 1880
- Biomphalaria
- tribe Planorbini Rafinesque, 1815
- PlanorbisPlanorbisPlanorbis 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.- Description :...
Müller, 1773
- Planorbis
- tribe Planorbulini Pilsbry, 1934
- Planorbula Haldeman, 1840 - type genus of tribe Planorbulini
- tribe Segmentinini F.C. Baker, 1945
- SegmentinaSegmentinaSegmentina is a genus of small, air-breathing, freshwater snails, aquatic gastropod mollusks or micromollusks in the family Planorbidae, the ramshorn snails....
Fleming, 1818 - type genus of tribe Segmentinini
- Segmentina
- tribe Ancylini Rafinesque, 1815
- subfamily Bulininae P. Fischer & Crosse, 1880
-
- Indoplanorbis Annandale & Prashad, 1920 - contains one species Indoplanorbis exustusIndoplanorbis exustusIndoplanorbis exustus is a species of air-breathing freshwater snail, an aquatic pulmonate gastropod mollusk in the family Planorbidae, the ram's horn snails. The species is the sole member of its genus and is widely distributed across the tropics. It serves as an important intermediate host for...
- PlanorbariusPlanorbariusPlanorbarius 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.-Species:...
Duméril, 1806 - PlanorbellaPlanorbellaPlanorbella 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.-Understanding the shell coiling:...
Haldeman, 1842 - MenetusMenetusMenetus is a North American genus of freshwater snails, aquatic pulmonate gastropod mollusks in the family Planorbidae, the ramshorn snails.-Species:Species within this genus include:subgenus Micromenetus F. C...
H. AdamsHenry Adams (zoologist)Henry Adams was an English naturalist and conchologist.With his brother Arthur Adams, also a noted conchologist, he wrote three volumes, 1858.-References:...
& A. AdamsArthur Adams (zoologist)Arthur Adams was an English physician and naturalist.Adams was assistant surgeon on board H.M.S. "Actaeon" in company with HMS Samarang in the British Navy during the survey of the Malay Archipelago, the Japan Sea, Korea and China,from 1843 to 1846. He edited the Zoology of the voyage of H.M.S....
, 1855- subgenus Dilatata Clessin, 1885
- Indoplanorbis Annandale & Prashad, 1920 - contains one species Indoplanorbis exustus
- tribe Bulinini P. Fischer & Crosse, 1880
- BulinusBulinusBulinus is a genus of small tropical freshwater snails, aquatic gastropod mollusks in the family Planorbidae, the ramshorn snails and their allies....
O. F. Müller, 1781 - type genus of subfamily Bulininae - GundlachiaGundlachiaGundlachia is a genus of minute freshwater snails or limpets, aquatic pulmonate gastropod mollusks in the family Planorbidae, the ram's horn snails and their allies....
Pfeiffer, 1849
- Bulinus
- tribe Coretini Gray, 1847
- Coretus Gray, 1847 - type genus of tribe Coretini
- tribe Miratestini P.1F. Sarasin, 1897
- MiratestaMiratestaMiratesta 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....
P. & F. Sarasin, 1897 - type genus of tribe Miratestini - Amerianna Strand, 1928
- FerrissiaFerrissiaFerrissia is a genus of air-breathing freshwater snail, a small freshwater limpet, an aquatic gastropod mollusk in the family Planorbidae, the ram's horn snails and their allies.-Species:Species within the genus Ferrissia include:...
Walker, 1903- Pettancyclus Iredale, 1943
- Miratesta
- tribe Plesiophysini Bequaert & Clench, 1939
- Plesiophysa P. Fischer, 1883 - type genus of tribe Plesiophysini
-
- subfamily Neoplanorbinae Hannibal, 1912
-
- NeoplanorbisNeoplanorbisNeoplanorbis is a genus of small, freshwater, air-breathing snails. They are aquatic pulmonate gastropod mollusks in the family Planorbidae, the ram's horn snails.Neoplanorbis is the type genus of the subfamily Neoplanorbinae.- Species :...
Pilsbry, 1906 - type genus of subfamily Neoplanorbinae
- Neoplanorbis
-
- subfamily Rhodacmeinae Walker, 1917
-
- Rhodacmea Walker, 1917 - type genus of subfamily Rhodacmeinae
-
subfamily ? (other genera not yet sorted here)
|
Glyptophysa Glyptophysa is a genus of small, left-handed or sinistral, air-breathing freshwater snails, aquatic pulmonate gastropod mollusks in the family Planorbidae.-Species:Species in the genus Glyptophysa include:* Glyptophysa petiti Crosse, 1872... Crosse, 1872 Helisoma Helisoma is a genus of freshwater air-breathing snail, a pulmonate gastropod mollusk in the family Planorbidae, the ram's horn snails.-Species:Species within the genus Helisoma include:... Swainson, 1840 Kessneria Kessneria is a genus of air-breathing freshwater snails, aquatic pulmonate gastropod mollusks in the family Planorbidae, the ram's horn snails.All species within family Planorbidae have sinistral shells.-Species:Species within this genus include:... Walker & Ponder Winston Ponder Winston F. Ponder B.Sc, M.Sc, Ph.D, D.Sc. is a noted malacologist from New Zealand who has named and described many marine animals, especially micromolluscs. He is a graduate of the University of Auckland, New Zealand.... , 2001 Leichhardtia Leichhardtia is a genus of air-breathing freshwater snails, aquatic pulmonate gastropod mollusks in the family Planorbidae, the ram's horn snails.All species within this genus and this family have sinistral shells.... Walker, 1988 Lentorbis Lentorbis is a genus of air-breathing freshwater snails, aquatic pulmonate gastropod mollusks in the family Planorbidae, the ram's horn snails.All species within family Planorbidae have sinistral shells.-Species:Species within this genus include:... Mandahl-Barth, 1954 |
Tom Iredale Tom Iredale was an English-born ornithologist and malacologist who had a long association with Australia, where he lived for most of his life. He was an autodidact who never went to university and lacked formal training... , 1943 Segmentorbis Segmentorbis is a genus of air-breathing freshwater snails, aquatic pulmonate gastropod mollusks in the family Planorbidae, the ram's horn snails.-Species:Species within this genus include:* Segmentorbis angustus... Mandahl-Barth, 1954 |
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
Henry Adams (zoologist)
Henry Adams was an English naturalist and conchologist.With his brother Arthur Adams, also a noted conchologist, he wrote three volumes, 1858.-References:...
& A. Adams
Arthur Adams (zoologist)
Arthur Adams was an English physician and naturalist.Adams was assistant surgeon on board H.M.S. "Actaeon" in company with HMS Samarang in the British Navy during the survey of the Malay Archipelago, the Japan Sea, Korea and China,from 1843 to 1846. He edited the Zoology of the voyage of H.M.S....
, 1855 is a synonym for Biomphalaria
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.Biomphalaria is the type genus of the tribe Biomphalariini....
.
Shell description
The shellsGastropod shell
The gastropod shell is a shell which is part of the body of a gastropod or snail, one kind of mollusc. The gastropod shell is an external skeleton or exoskeleton, which serves not only for muscle attachment, but also for protection from predators and from mechanical damage...
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
Limpet
Limpet is a common name for a number of different kinds of saltwater and freshwater snails ; it is applied to those snails that have a simple shell which is more or less conical in shape, and either is not spirally coiled, or appears not to be coiled in the adult snails.The name limpet is most...
-like.
All coiled shell Planorbidae are sinistral
Sinistral
Sinistral and dextral are scientific terms that describe chirality or relative direction in a number of disciplines.The terms are derived from the Latin words for “left” and “right” ....
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 overlap.
The aperture
Aperture (mollusc)
The aperture is an opening in certain kinds of mollusc shells: it is the main opening of the shell, where part of the body of the animal emerges for locomotion, feeding, etc....
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
Parietal callus
A parietal callus is a feature of the shell anatomy of some groups of snails, i.e. gastropods. It is a thickened calcareous deposit which may be present on the parietal wall of the aperture of the adult shell. The parietal wall is the margin of the aperture and part of the wall of the body whorl...
.
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
Operculum (gastropod)
The operculum, meaning little lid, is a corneous or calcareous anatomical structure which exists in many groups of sea snails and freshwater snails, and also in a few groups of land snails...
to close the shell aperture.
Sinistral shells
Gastropod shell
The gastropod shell is a shell which is part of the body of a gastropod or snail, one kind of mollusc. The gastropod shell is an external skeleton or exoskeleton, which serves not only for muscle attachment, but also for protection from predators and from mechanical damage...
s 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
Spire (mollusc)
A spire is a descriptive term for part of the coiled shell of mollusks. The word is a convenient aid in describing shells, but it does not refer to a very precise part of shell anatomy: the spire consists of all of the whorls except for the body whorl...
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 umbilicusUmbilicus (mollusk)The umbilicus of a shell is the axially aligned, hollow cone-shaped space within the whorls of a coiled mollusc shell. The term umbilicus is often used in descriptions of gastropod shells, i.e...
facing upwards - The spireSpire (mollusc)A spire is a descriptive term for part of the coiled shell of mollusks. The word is a convenient aid in describing shells, but it does not refer to a very precise part of shell anatomy: the spire consists of all of the whorls except for the body whorl...
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
Aperture (mollusc)
The aperture is an opening in certain kinds of mollusc shells: it is the main opening of the shell, where part of the body of the animal emerges for locomotion, feeding, etc....
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
Aperture (mollusc)
The aperture is an opening in certain kinds of mollusc shells: it is the main opening of the shell, where part of the body of the animal emerges for locomotion, feeding, etc....
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
Contrary to the case in most other molluscs, the blood of ram's-horn snails contains hemoglobinHemoglobin
Hemoglobin is the iron-containing oxygen-transport metalloprotein in the red blood cells of all vertebrates, with the exception of the fish family Channichthyidae, as well as the tissues of some invertebrates...
.
As a result these animals are able to breathe oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
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 of planorbids live only in fresh water. A minority of species are able to survive in brackish water.Geological history
Ancestors of ramshorn snails are known with certainty since the JurassicJurassic
The Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
period. Modern taxa developed since the Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
.
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
Jurassic
The Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
period.