The shell, penis, and female reproductive organs of six molecularly distinct Bythinella species from Romania are described. The species were found by the authors in their earlier study based on mt DNA COI, and rRNA ITS-1. None of the species is identical with B. austriaca (Frauenfeld, 1857). Two of them are identified as B. dacica Grossu, 1946 and B. molcsanyi H. Wagner, 1941. The other four species are described as new. The occurrence of B. melanostoma (Brancsik, 1889), and of B. austriaca ehrmanni Pax, 1938 in Romania is rejected. The sympatric occurrence of two species in four studied springs was stressed. The molecular distinctness of the studied species is not reflected in their morphology, the morphological differences are poorly marked, their variability ranges overlapping.