An SEM study of the nuchal organ in Daphnia himalaya (nov. sp.) embryos and neonates collected from the Khumbu region (Nepalese Himalayas)

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Marina MANCA
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Zooplankton from the Khumbu region in Nepal are rarely studied, and little is known regarding their morphology and physiology. During the EV-K2-CNR Project, a collaboration between the Government of the Republic of Italy and the Nepal Academy of Science and Technology (NAST) as part of “The long distance transport of micro-pollutants”, zooplankton samples revealed the presence of small head shields’ remains in the sediment possessing a hole in the dorsal margin. This observation led to the hypothesis that Daphnia himalaya neonates must possess a nuchal organ for osmoregulation in these alpine lakes. Here we report the presence of a nuchal organ in embryos and neonates, and explore its development, noting that the nuchal organ is retained up until the first post-embryonic moult. We also examine the chemistry of the lakes and in particular their conductivity, which is lower in lakes having D. himalaya than in lakes that do not (16 μS and 32 μS cm-1 respectively).

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