Subfossil remains of an unknown chydorid (Anomopoda : Chydoridae) from Finland

Subfossil remains of an unknown chydorid taxon were found in sediments of t hree lake basins in Finland. Two of the sites lie in southern Finland and o ne in NW Finnish Lapland. Similar remains are also known from four lakes in eastern Finland. The headshields are small, with a broadly rounded posteri or margin and an attenuated rostrum. The headshields resemble those of Rhyn chotalona falcata Sars, but have a unique pore arrangement. There is one ov al median pore near the posterior margin and two lateral pores which are di splaced quite far in position. The shell is very small and has faint, longi tudinal striae. Also, unknown postabdomens were found. These resemble posta bdomen of R. falcata in shape but had 5-6 pairs of teeth instead of the 2 s een in R. falcata. The age of the remains varies between ca. 8500 C-14 yr B P and recent decades. The species appears to have been present in the entir e country during most of the Holocene. On the basis of the pore arrangement , the new species cannot be put into any previously known genus. A tentativ e name Unapertura latens n. sp. is suggested until intact specimens are fou nd and described.