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| image = Notodoris minor.jpg | image_caption = ''Aegires minor'' | regnum = Animalia | phylum = Mollusca | classis = Gastropoda | unranked_familia = clade Heterobranchia informal group "Opisthobranchia" | unranked_familia_authority = Milne-Edwards, 1848 | subdivision_ranks = Included groups | subdivision = clade Cephalaspidea clade Thecosomata clade Gymnosomata clade Aplysiomorpha group Acochlidiacea clade Sacoglossa group Cylindrobullida clade Umbraculida clade Nudipleura }} Opisthobranchs are a large and diverse group of specialized complex gastropods previously united in the subclass Opisthobranchia, but no longer considered to represent a monophyletic grouping because it contains the land snails and slugs, the Pulmonata.〔 Euopisthobranchia is a revised collection of opisthobranchs that ''is'' monophyletic, but this group leaves out some "traditional" opisthobranchs including the Sacoglossa and the Acochlidiacea.〔 The subclass Heterobranchia now contains the species which previously were assigned to Opisthobranchia plus the Pulmonata. The Opisthobranchia included species in the order Cephalaspidea (bubble shells and headshield slugs), the sacoglossans, the anaspidean sea hares, the pelagic sea angels, the sea butterflies, and many families of Nudibranchia.〔 ''Opisthobranch'' means "gills behind" (and to the right) of the heart. In contrast, ''Prosobranch'' means ''gills in front'' (of the heart). Opisthobranchs are characterized by two pairs of tentacles and a single gill behind and to the right of the heart. Opisthobranchia are known from as early as the Carboniferous.〔(in Czech) Pek I., Vašíček Z., Roček Z., Hajn. V. & Mikuláš R.: ''Základy zoopaleontologie''. - Olomouc, 1996. 264 pp., ISBN 80-7067-599-3.〕 == Taxonomy == Under the old classification system by Johannes Thiele in 1931, class Gastropoda was divided into three subclasses; Prosobranchia, Pulmonata and Opisthobranchia. The latter two were later combined into a single order. The current classification of the gastropods is more complicated, with the following subclasses:〔Gofas, S. (2014). Gastropoda. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=101 on 2015-02-12〕 * Subclass Caenogastropoda * Subclass Cocculiniformia * Subclass Heterobranchia * Subclass Neomphalina * Subclass Neritimorpha * Subclass Patellogastropoda * Subclass Vetigastropoda * Subclass Gastropoda incertae sedis 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「opisthobranchia」の詳細全文を読む スポンサード リンク
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