Heterobranchia, the ''heterobranchs'' (meaning "different-gilled snails"), is a
taxonomic clade
A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English ter ...
of
snail
A snail is, in loose terms, a shelled gastropod. The name is most often applied to land snails, terrestrial pulmonate gastropod molluscs. However, the common name ''snail'' is also used for most of the members of the molluscan class ...
s and
slugs
Slug, or land slug, is a common name for any apparently shell-less terrestrial molluscs, terrestrial gastropod mollusc. The word ''slug'' is also often used as part of the common name of any gastropod mollusc that has no shell, a very reduced ...
, which includes
marine
Marine is an adjective meaning of or pertaining to the sea or ocean.
Marine or marines may refer to:
Ocean
* Maritime (disambiguation)
* Marine art
* Marine biology
* Marine debris
* Marine habitats
* Marine life
* Marine pollution
Military ...
,
aquatic and
terrestrial gastropod
The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda ().
This class comprises snails and slugs from saltwater, from freshwater, and from land. T ...
mollusk
Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is e ...
s.
Heterobranchia is one of the main clades of gastropods. Currently Heterobranchia comprises three informal groups: the
lower heterobranchs, the
opisthobranchs and the
pulmonates.
[Bouchet P. & Rocroi J.-P. (Ed.); Frýda J., Hausdorf B., Ponder W., Valdes A. & Warén A. 2005. ''Classification and nomenclator of gastropod families''. Malacologia: International Journal of Malacology, 47(1-2). ConchBooks: Hackenheim, Germany. . . 397 pp. http://www.vliz.be/Vmdcdata/imis2/ref.php?refid=78278]
Diversity
The three subdivisions of this large clade are quite diverse:
* The
Lower Heterobranchia includes shelled marine and freshwater species.
*
Opisthobranchia
Opisthobranchs () is now an informal name for a large and diverse group of specialized complex gastropods which used to be united in the subclass Opisthobranchia. That taxon is no longer considered to represent a monophyletic grouping.
Euopi ...
are almost all marine species, some
shelled and some not. The internal organs of the opisthobranchs have undergone detorsion (unwinding of the viscera that were twisted during
torsion).
* The
Pulmonata
Pulmonata or pulmonates, is an informal group (previously an Order (biology), order, and before that a Class (biology), subclass) of snails and slugs characterized by the ability to breathe air, by virtue of having a Respiratory system of gastro ...
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
operculum and are
hermaphroditic
In reproductive biology, a hermaphrodite () is an organism that has both kinds of reproductive organs and can produce both gametes associated with male and female sexes.
Many taxonomic groups of animals (mostly invertebrates) do not have s ...
.
Taxonomy
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. Gray, 1840) considered Heterobranchia to consist of only marine gastropods, and conceptualized it as a borderline category, intermediate between the
Opisthobranchia
Opisthobranchs () is now an informal name for a large and diverse group of specialized complex gastropods which used to be united in the subclass Opisthobranchia. That taxon is no longer considered to represent a monophyletic grouping.
Euopi ...
&
Pulmonata
Pulmonata or pulmonates, is an informal group (previously an Order (biology), order, and before that a Class (biology), subclass) of snails and slugs characterized by the ability to breathe air, by virtue of having a Respiratory system of gastro ...
, 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
A protoconch (meaning first or earliest or original shell) is an embryonic or larval shell which occurs in some classes of molluscs, e.g., the initial chamber of an ammonite or the larval shell of a gastropod. In older texts it is also called " ...
, 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.
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
Euopisthobranchia and
Panpulmonata.
A
cladogram
A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to ...
showing phylogenic relations of Heterobranchia as proposed by Jörger et al. (2010):
References
Further reading
* Dinapoli A. (2009). ''Phylogeny and Evolution of the Heterobranchia (Mollusca, Gastropoda)''. Thesis, Frankfurt am Main, 176 pp
PDF
*
{{Taxonbar, from=Q133143
Gastropod taxonomy
Protostome unranked clades
Taxa named by John Edward Gray