Pontohedyle
| Pontohedyle | |
|---|---|
 |
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| live Pontohedyle milaschewitchii ot = oral tentacles, ey = eyes, dg = digestive gland. |
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| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Mollusca |
| Class: | Gastropoda |
| (unranked): | clade Heterobranchia clade Euthyneura clade Panpulmonata clade Acochlidiacea clade Microhedylacea |
| Family: | Microhedylidae |
| Genus: |
Pontohedyle Golikov & Starobogatov, 1972 |
| Diversity | |
| at least 12 cryptic species (3 valid, at least 9 undescribed) | |
| Synonyms | |
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Gastrohedyle Rankin, 1979 |
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Gastrohedyle Rankin, 1979
Mancohedyle Salvini-Plawen, 1973
Maraunibina Rankin, 1979
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.
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) 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.
With its vermiform body, a putatively multi-functional radula, ‘simplified’ organ systems and a special fast and imprecise mode of sperm transfer, Pontohedyle reflects a meiofaunal slug lineage highly adapted to its interstitial habitat.
Pontohedyle is morphologically well-defined genus of meiofaunal slugs. Specimens of Pontohedyle are externally uniform and easily distinguishable from other acochlids by the lack of rhinophores and the bow-shaped oral tentacles.Pontohedyle typically bear monaxone, rodlet-like spicules distributed randomly and frequently accumulated between the oral tentacles. No diagnostic differences in external morphology or spicules could be detected between the collected populations apart from eyes externally visible or not. Comparative SEM-examination of the available radulae revealed two types of the typically hook-shaped radula: a lateral tooth without a denticle (Pontohedyle verrucosa) or with a denticle (Pontohedyle milaschewitchii).
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