{{Short description|Group of molluscs}} {{Automatic_taxobox | image = Pleurobranchaea meckelii.jpg | image_caption = A live individual of ''Pleurobranchaea meckelii''; the gill (or ctenidium) is visible in this view of the right-hand side of the animal | taxon = Notaspidea | authority = P. Fischer, 1883 }}
'''Notaspidea''', also known as the '''sidegill slugs''', is an artificial grouping of sea slugs which is now split into two unrelated groups, the Umbraculida and the Pleurobranchomorpha.<ref>Gofas, S. (2014). Notaspidea. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=1754 on 2015-02-12</ref>
==Taxonomic history== Notaspidea, also known as the '''sidegill slugs''', was a suborder which included both sea slugs and sea snails or false limpets, marine opisthobranch gastropod molluscs in the subclass Orthogastropoda. However, in the newer taxonomy of Bouchet & Rocroi (2005), the families Umbraculidae and Tylodinidae belong to the superfamily Umbraculoidea Dall, 1889, part of the clade Umbraculida. Grande ''et al.'' (2004) found Umbraculoidea to be a sister clade to the Cephalaspidea (Acteonoidea excluded).<ref>{{cite journal |author1=Grande C. |author2=J. Templado |author3=J.L. Cervera |author4=R. Zardoya | title=Phylogenetic relationships among Opisthobranchia (Mollusca, Gastropoda) based on mitochondrial cox1, tmV, and rmL genes| journal=Molecular Phylogenetics and Evolution| year=2004| volume=33| pages=378–388| doi=10.1016/j.ympev.2004.06.008 | pmid=15336672 | issue=2}}</ref>
The families Tylodinidae and Umbraculidae have large limpet-like external shells and a small mantle, while the species in the family Pleurobranchidae have a prominent mantle and an internal shell that becomes reduced or is lost in adults.<ref name="Notaspidea">{{cite journal | author=R. Willan| title=Phylogenetic systematics of the Notaspidea (Opisthobranchia) with a reappraisal of families and genera| journal=Am. Malacol. Bull.| year=1987| volume=5| pages=215–241}}</ref> Many species produce mantle secretions as a chemical defense against predators <ref name="mucus">{{cite journal |author1=Aldo Spinella |author2=Ernesto Mollo |author3=Enrico Trivellone |author4=Guido Cimino | title=Testudinariol A and B, two unusual triterpenoids from the skin and the mucus of the marine mollusc ''Pleurobrancus testudinarius''.| journal=Tetrahedron|date=December 1997| volume=53| issue=49| pages=16891–16896| doi=10.1016/S0040-4020(97)10124-7| doi-access=free}}</ref>
==Families== * Pleurobranchidae Menke, 1828 * Tylodinidae Gray, 1847 * Umbraculidae Dall, 1889
== Notes == {{Reflist}}
==References== * {{ITIS |id=78119 |taxon=Notaspidea}} * Powell A. W. B., ''New Zealand Mollusca'', William Collins Publishers Ltd, Auckland, New Zealand 1979 {{ISBN|0-00-216906-1}}
{{Taxonbar|from=Q141484}} {{Authority control}}
Category:Obsolete gastropod taxa Category:Taxa named by Paul Henri Fischer