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Pontohedyle
''Pontohedyle'' is a genus of sea slugs, acochlidians, shell-less marine gastropod mollusks in the family Microhedylidae. Sea slugs in this genus are highly simplified and uniform.〔
== Distribution ==
The genus ''Pontohedyle'' shows a circumtropical distribution with a single derived species (Mediterranean/ Black Sea ''Pontohedyle milaschewitchii'') inhabiting temperate waters.〔 In the absence of a fossil record for meiofaunal slugs, the only available estimate for divergence times derives from a molecular clock approach, calibrated with shelled heterobranch fossils.〔 Jörger et al. (2010)〔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. .〕 estimated the origin of the genus ''Pontohedyle'' to the late Cretaceous, 84 mya (95% confidence interval ranging from 160–60 mya), providing a rough estimation of how much time was available for diversification and circum-global dispersal of ''Pontohedyle'' slugs.〔
''Pontohedyle'' has never been found in colder waters despite a well-studied meiofauna and hydrographic conditions similar to the Mediterranean.〔 The distribution of ''Pontohedyle'' might be constrained by ancestry from warm-water adapted animals.〔 Considering the estimated mid to late Mesozoic origin and the recent primarily tropical distribution pattern in ''Pontohedyle'', it is most likely that this meiofaunal slug clade originated in Tethyan waters.〔
(Map of ''Pontohedyle'' distribution ).
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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