Euopisthobranchia is a taxonomic
clade
In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...
of
snails
A snail is a shelled gastropod. The name is most often applied to land snails, terrestrial molluscs, terrestrial pulmonate gastropod molluscs. However, the common name ''snail'' is also used for most of the members of the molluscan class Gas ...
and
slugs in the clade
Heterobranchia within the clade
Euthyneura
Euthyneura is a taxonomic infraclass of snails and slugs, which includes species exclusively from marine, aquatic and terrestrial gastropod mollusks in the clade Heterobranchia.
Euthyneura are characterised by several autapomorphies, bu ...
.
This clade was established as a new taxon by Jörger et al. in October 2010.
Euopisthobranchia is a
monophyletic
In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria:
# the grouping contains its own most recent co ...
portion of the
Opisthobranchia as that taxon was traditionally defined but is not a replacement name for that group as several marine opisthobranch orders including
Nudibranchia,
Sacoglossa and
Acochlidiacea
Acochlidiacea, common name acochlidians, are a Taxonomy (biology), taxonomic clade of very unusual sea snails and sea and freshwater slugs, aquatic animal, aquatic gastropod mollusks within the large clade Heterobranchia. Acochlidia is a variant ...
are not included.
Euopisthobranchia consist of the following taxa:
*
Umbraculoidea
*
Anaspidea
*
Runcinacea
*
Pteropoda
*
Cephalaspidea s.s.
Gizzard
Previous studies discussed the
gizzard (i.e. a muscular oesophageal crop lined with cuticula) with gizzard plates as homologous
apomorphic structures supporting a clade composed of Cephalaspidea s.s., Pteropoda and Anaspidea.
A gizzard with gizzard plates probably originated in herbivorous taxa in which it worked like a grinding mill, thus might be secondarily reduced in carnivorous groups within Cephalaspidea s.s. and Gymnosomata.
Klussmann-Kolb and Dinapoli considered the gizzard in Umbraculoidea as non-homologous with the one in the previous groups, on account of the absence of gizzard plates or spines.
This contradicted Salvini-Plawen and Steiner, who had proposed the gizzard to be a
synapomorphy
In phylogenetics, an apomorphy (or derived trait) is a novel Phenotypic trait, character or character state that has evolution, evolved from its ancestral form (or Plesiomorphy and symplesiomorphy, plesiomorphy). A synapomorphy is an apomorphy sh ...
of the larger clade of
Paratectibranchia (Pteropoda, Cephalaspidea and Anaspidea) and
Eleutherobranchia, secondarily lost in Nudipleura but still present in Umbraculoidea.
As coded in Wägele and Klussmann-Kolb, phylogenetic hypothesis by Jörger et al. (2010)
supports homology of the gizzard in Umbraculoidea with the gizzard with gizzard plates and spines in the other euopisthobranchian taxa.
Thus, the structure is proposed as a synapomorphy of Euopisthobranchia.
Cladogram
A
cladogram
A cladogram (from Greek language, Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an Phylogenetic tree, evolutionary tree because it does not s ...
showing phylogenic relations of the Heterobranchia as proposed by Jörger et al. (2010):
See also
*
Changes in the taxonomy of gastropods since 2005#Heterobranchia
*
Heterobranchia#2010 taxonomy
*
Acochlidiacea#2010 taxonomy
References
This article incorporates CC-BY-2.0 text from the reference.
{{Taxonbar, from=Q5365190