Heterobranchia
Encyclopedia
Heterobranchia, the heterobranchs (meaning "different-gilled snails") or Euthyneura
, is a taxonomic clade
of snail
s and slugs, which includes species from the sea, the land and freshwater; marine
, aquatic
and terrestrial
gastropod mollusks.
Heterobranchia is one of the main clades of gastropods, containing the largest number of species of any of the main clades. Currently Heterobranchia comprises three informal groups: the Lower Heterobranchia
, the Opisthobranchia
and the Pulmonata
, also known as the lower heterobranchs, the opisthobranchs and the pulmonates.
, 1840) considered Heterobranchia to consist of only marine gastropods, and conceptualized it as a borderline category, intermediate between the Opisthobranchia
& Pulmonata
, and all the other gastropods.
The (sometimes recognized) category Heterostropha
within the Heterobranchia, which includes such families as Architectonicidae
, the sundial or staircase snails, is primarily characterized by a shell which has a heterostrophic protoconch
, in other words the apical whorls are coiled in the opposite plane to the adult whorls. The classification of this group was revised by Ponder
& Warén in 1988.
According to the older taxonomy of the Gastropoda (Ponder & Lindberg, 1997)
the Heterobranchia were ranked as a superorder.
and Panpulmonata
.
A cladogram
showing phylogenic relations of Heterobranchia as proposed by Jörger et al. (2010):
Euthyneura
Euthyneura is a taxonomic clade of snails and slugs, which includes species from the sea, the land and freshwater; marine, aquatic and terrestrial gastropod mollusks in the clade Heterobranchia....
, is a taxonomic clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
of snail
Snail
Snail is a common name applied to most of the members of the molluscan class Gastropoda that have coiled shells in the adult stage. When the word is used in its most general sense, it includes sea snails, land snails and freshwater snails. The word snail without any qualifier is however more often...
s and slugs, which includes species from the sea, the land and freshwater; marine
Marine (ocean)
Marine is an umbrella term. As an adjective it is usually applicable to things relating to the sea or ocean, such as marine biology, marine ecology and marine geology...
, 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...
and terrestrial
Terrestrial animal
Terrestrial animals are animals that live predominantly or entirely on land , as compared with aquatic animals, which live predominantly or entirely in the water , or amphibians, which rely on a combination of aquatic and terrestrial habitats...
gastropod mollusks.
Heterobranchia is one of the main clades of gastropods, containing the largest number of species of any of the main clades. Currently Heterobranchia comprises three informal groups: the Lower Heterobranchia
Lower Heterobranchia
Lower Heterobranchia, also known as the Allogastropoda, is a group of rather specialized, highly-evolved sea slugs and sea snails, within the clade Heterobranchia...
, the Opisthobranchia
Opisthobranchia
Opisthobranchs are a large and diverse group of specialized complex marine gastropods previously united under Opisthobranchia within the Heterobranchia, but no longer considered to represent a monophyletic grouping...
and the Pulmonata
Pulmonata
The Pulmonata, or "pulmonates", are an informal group of snails and slugs characterized by the ability to breathe air, by virtue of having a pallial lung instead of a gill, or gills...
, also known as the lower heterobranchs, the opisthobranchs and the pulmonates.
Diversity
The three subdivisions of this large clade are quite diverse:- The Lower HeterobranchiaLower HeterobranchiaLower Heterobranchia, also known as the Allogastropoda, is a group of rather specialized, highly-evolved sea slugs and sea snails, within the clade Heterobranchia...
includes shelled marine and freshwater species.
- OpisthobranchiaOpisthobranchiaOpisthobranchs are a large and diverse group of specialized complex marine gastropods previously united under Opisthobranchia within the Heterobranchia, but no longer considered to represent a monophyletic grouping...
are almost all marine species, some shelledGastropod shellThe 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...
and some not. The internal organs of the opisthobranchs have undergone detorsion (unwinding of the viscera that were twisted during torsionTorsion (gastropod)Torsion is an anatomical event which takes place during the very early part of the life of snails and slugs of all kinds. In other words, torsion is a gastropod synapomorphy which occurs in all gastropods during larval development. Torsion is the rotation of the visceral mass, mantle and shell 180˚...
).
- The PulmonataPulmonataThe Pulmonata, or "pulmonates", are an informal group of snails and slugs characterized by the ability to breathe air, by virtue of having a pallial lung instead of a gill, or gills...
includes the majority of land snails and slugs, many freshwater snails, and a small number of marine species. The mantle cavity of the Pulmonata is modified into an air-breathing organ. They are also characterized by detorsion and a symmetrically-arranged nervous system. The pulmonates almost always lack an operculumOperculum (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...
and are hermaphroditic.
Older taxonomy
The families currently included in Heterobranchia have historically been placed in many different parts of the taxonomic class of gastropods. Earlier authors (such as J.E. GrayJohn Edward Gray
John Edward Gray, FRS was a British zoologist. He was the elder brother of George Robert Gray and son of the pharmacologist and botanist Samuel Frederick Gray ....
, 1840) considered Heterobranchia to consist of only marine gastropods, and conceptualized it as a borderline category, intermediate between the Opisthobranchia
Opisthobranchia
Opisthobranchs are a large and diverse group of specialized complex marine gastropods previously united under Opisthobranchia within the Heterobranchia, but no longer considered to represent a monophyletic grouping...
& Pulmonata
Pulmonata
The Pulmonata, or "pulmonates", are an informal group of snails and slugs characterized by the ability to breathe air, by virtue of having a pallial lung instead of a gill, or gills...
, and all the other gastropods.
The (sometimes recognized) category Heterostropha
Heterostropha
Heterostropha was a previously used taxonomic category, an order of sea snails, within the superorder Heterobranchia. In the most current gastropod taxonomy, that of Bouchet & Rocroi, this taxon is no longer in use....
within the Heterobranchia, which includes such families as Architectonicidae
Architectonicidae
Architectonicidae, common name the staircase shells or sundials, are a family of sea snails, marine gastropod mollusks in the informal group "Lower Heterobranchia" of the clade Heterobranchia....
, the sundial or staircase snails, is primarily characterized by a shell which has a heterostrophic protoconch
Protoconch
A protoconch is an embryonic or larval shell of some classes of molluscs, e.g., the initial chamber of an ammonite or the larval shell of a gastropod...
, in other words the apical whorls are coiled in the opposite plane to the adult whorls. The classification of this group was revised by 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....
& Warén in 1988.
According to the older taxonomy of the Gastropoda (Ponder & Lindberg, 1997)
Taxonomy of the Gastropoda (Ponder & Lindberg, 1997)
The taxonomy of the Gastropoda, as revised by Winston Ponder and David R. Lindberg in 1997, is an older taxonomy of the class Gastropoda, the class of molluscs consisting of all snails and slugs...
the Heterobranchia were ranked as a superorder.
2005 taxonomy
Heterobranchia is currently one of the main clades of gastropods. For a detailed taxonomy, see Taxonomy of the Gastropoda (Bouchet & Rocroi, 2005)#Clade Heterobranchia.2010 taxonomy
Jörger et al. (2010) have redefined major groups within the Heterobranchia: they created the new clades EuopisthobranchiaEuopisthobranchia
Euopisthobranchia is a taxonomic clade of snails and slugs in the clade Heterobranchia within the clade Euthyneura.Euopisthobranchia was established as a new taxon by Jörger et al...
and Panpulmonata
Panpulmonata
Panpulmonata is a taxonomic clade of snails and slugs in the clade Heterobranchia within the clade Euthyneura.Panpulmonata was established as a new taxon by Jörger et al...
.
A cladogram
Cladogram
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...
showing phylogenic relations of Heterobranchia as proposed by Jörger et al. (2010):
Further reading
- Dinapoli A. (2009). Phylogeny and Evolution of the Heterobranchia (Mollusca, Gastropoda). Thesis, Frankfurt am Main, 176 pp. PDF.
- Dinapoli A. & Klussmann-Kolb A. (2010). "The long way to diversity – Phylogeny and evolution of the Heterobranchia (Mollusca: Gastropoda)". Molecular Phylogenetics and EvolutionMolecular Phylogenetics and EvolutionMolecular Phylogenetics and Evolution is a peer-reviewed scientific journal of evolutionary biology and phylogenetics. The journal is edited by D.E. Wildman.-Indexing:The journal is indexed in:*EMBiology*Journal Citation Reports*Scopus*Web of Science...
55(1): 60-76. doi:10.1016/j.ympev.2009.09.019.