Description of the subfossil head shield of Alona protzi Hartwig 1900 (Anomopoda, Chydoridae) and the environmental characteristics of its finding sites

This pa per gives a de scrip tion of the head shield of Alona protzi, a rare spe cies of Cla do cera (wa ter fleas) whose separated head shield has not yet been de scribed in de tail. Sub fos sil head shields of A. protzi were found in sedi ment cores taken from lakes in Den mark, Swe den, Fin land, Es to nia and Po land. De spite the rar ity of the spe cies this sug gests a wide dis tri bu tion of A. protzi in north ern Europe. The ecol ogy of A. protzi is poorly known. The en vi ron mental spec -trum of the find ing sites was wide and ranged from rela tively nu tri ent poor clear wa ter lakes to eutrophic tur bid wa terlakes, in di cat ing that A. protzi is not nar rowly re stricted. Most of the lakes were, how ever, meso- eutrophic with neu tral to high pH, and with a rela tively low abun dance of sub merged mac ro phytes. How ever, we can not ex clude the pos si bility that A. protzi mainly lives in ground wa ter and is only oc ca sion ally trans ported into lakes.