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''Arion fuscus, ''aka "Dusky Arion", is a species of small air-breathing land slug, a terrestrial pulmonate gastropod mollusk in the family Arionidae, the roundback slugs. ''Arion subfuscus'' (Draparnaud, 1805) is considered by some authors to be a partial synonym for ''Arion fuscus''.〔(Arbeitskreis Mollusken NRW )〕 ''Arion subfuscus'' (Draparnaud, 1805) and ''A. fuscus'' (Müller, 1774) have very similar morphology and have overlapping distributional ranges in northwestern Europe. ''Arion fuscus'' is widespread throughout Central, North and East Europe whereas ''A. subfuscus'' is restricted to West Europe.(For practical purposes the two are synonyms in Germany and in the Czech Republic.) The two taxa are referred to as the species complex ''Arion subfuscus''/''fuscus'' both members having several evolutionary lineages.They are only separable by alloenzyme analysis and gonad type. ==Description== Note. In slugs it is often difficult to establish good criteria for identifying species using external features or internal features, as colouration can be quite variable, and the rather plastic anatomy makes diagnostic anatomical features difficult to establish. A 50-70 mm. roundback slug. It is brown in colour, ranging from black-brown through olive-brown to orange and bright reddish-orange. Darker lateral bands are present.Dark pigment reaches under the pneumostome from back to front. The foot fringe is pale with thin lines.The sole is uniformly pale/translucent.The tentacles are pale.It does not contract into a bell shape when stimulated. Differs from other ''Arion'' species in its yellow-orange body mucus. Genitalia:Atrium about half diameter of spermatheca, spermatheca spherical, oviduct large and swollen like in ''Arion lusitanicus''〔(Animalbase (Welter-Schultes) ) 〕 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「Arion fuscus」の詳細全文を読む スポンサード リンク
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