An unusual type of Daphnia head shields from plankton and sediments of Himalayan lakes

Abstract

The paper reports the finding of a particular type of Daphnia (Ctenodaphnia, Dybowski & Grochowski 1895) head shields, found in the plankton and in the sediments of two lakes in the Khumbu Region (Nepalese Himalayas). The capsules, all of the smallest size, were characterised by the presence of a hole in the medio-dorsal region, behind the posterior median groove. The location of the hole suggests a link with the nuchal organ, which we found in the neonates of the species. The finding is important for taxonomy and provides information for discussing the current hypothesis on the biogeography of the Ctenodaphnia subgenus. Being well preserved in sediment cores, the capsules are useful tools for reconstructing past phases of active reproduction which occurred also in the past.