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Scenella
''Scenella'' is an extinct genus of fossil invertebrate animal which is generally considered to be a mollusc; at various times it has been suggested that this genus belongs with the gastropods, the monoplacophorans, or the helcionellids, although no firm association with any of these classes has been established. An affinity with the hydrozoa (as a flotation device) has been considered,〔 although some authors oppose this hypothesis. A gastropod affinity is defended on the basis of six pairs of internal muscle scars, whilst the serially-repeated nature of these scars suggests to other authors a monoplacophoran affinity.〔 However the specimens showing this scarring have not been convincingly shown to belong to the genus ''Scenella''.〔 A similarity to the Ediacaran ''Ovatoscutum'' has also been drawn.
==Description==
The shell of ''Scenella'' is elongated along its anterior-posterior axis, and comprises concentric rings around a conical central peak. Radial and concentric corrugations exist in some species.〔 Some specimens are preserved as organic films, others appear to have been infilled with calcite.〔 They are usually preserved point-upwards, with their long axes consistently oriented; this probably represents their most stable position under their depositional current.〔 Soft parts have never been reported in association with ''Scenella'', suggesting that the preserved fragments separated quickly from the associated tissue prior to burial.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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