Euopisthobranchia

Euopisthobranchia is a taxonomic clade of snails and slugs in the clade Heterobranchia within the clade Euthyneura.

Euopisthobranchia
Chelidonura pallida
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Mollusca
Class:	Gastropoda
Subterclass:	Tectipleura
Clade:	Euopisthobranchia Jörger et al., 2010[1]
Taxonomic subdivisions
See text

This clade was established as a new taxon by Jörger et al. in October 2010.^[1] Euopisthobranchia is a monophyletic 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 are not included.^[1]

Euopisthobranchia consist of the following taxa:^[1]

• 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.^[1] 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.^[1] 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.^[1] This contradicted Salvini-Plawen and Steiner, who had proposed the gizzard to be a synapomorphy of the larger clade of Paratectibranchia (Pteropoda, Cephalaspidea and Anaspidea) and Eleutherobranchia, secondarily lost in Nudipleura but still present in Umbraculoidea.^[1] As coded in Wägele and Klussmann-Kolb, phylogenetic hypothesis by Jörger et al. (2010)^[1] supports homology of the gizzard in Umbraculoidea with the gizzard with gizzard plates and spines in the other euopisthobranchian taxa.^[1] Thus, the structure is proposed as a synapomorphy of Euopisthobranchia.^[1]

Cladogram

A cladogram showing phylogenic relations of the Heterobranchia as proposed by Jörger et al. (2010):^[1]

Heterobranchia

Lower Heterobranchia (including Acteonoidea) - Lower Heterobranchia does not form a clade in the study by Jörger et al. (2010):[1] Euthyneura Nudipleura Nudibranchia Pleurobranchomorpha Euopisthobranchia Umbraculoidea Cephalaspidea s.s. Runcinacea Anaspidea Pteropoda (pteropods include two clades: Gymnosomata and Thecosomata) Panpulmonata Sacoglossa Siphonarioidea Glacidorboidea Amphiboloidea Pyramidelloidea Hygrophila Acochlidiacea Eupulmonata Stylommatophora Systellommatophora Ellobioidea Otinoidea Trimusculoidea

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.^[1]

1. Jörger K. M., Stöger I., Kano Y., Fukuda H., Knebelsberger T. & Schrödl M. (2010). "On the origin of Acochlidia and other enigmatic euthyneuran gastropods, with implications for the systematics of Heterobranchia". BMC Evolutionary Biology 10: 323. doi:10.1186/1471-2148-10-323.