Genus Congeria with three exctanct species which live in the subterranean habitats of the Dinaric karst is the only stygobiotic taxon of bivalves. Unlike its surface relatives, these bivalves lost tissue pigmentation, which is feature that many subterranean animals have in common. The molecular causes of the loss of pigmentation in animals is scarcely known. The aim of this research is to identify molecular cause of the loss of pigmentation in genus Congeria by conmparing primary structure of DNA and protein homologues of tyrosinase between stygobiotic and two surface genera (Dreissena, Mytilopsis) of the bivalve family Dreissenidae. It is known in literature that tyrosinase is an enzyme important for pigmentation in bivalves and that it catalyses the first step in the biosynthesis of melanine. The sequences of tyrosinase of bivalves of the family Dreissenidae were found by searching the transcriptome (sequenced before) using tool called PIA (phylogenetically-informed annotation) and by sequencing products, fragments of tyrosinase homologs, amplified using polymerase chain reaction (PCR). The enzymatic activity of phenoloxidases, to which tyrosinase belongs, was tested by spectrophotometric analysis. The pyhlogenetic analysis of tyrosinases of this bivalve family was also performed. The unique features of tyrosinase sequences of Congeria jalzici in comparison to other members of the family and the lower phenoloxidase activity, compared to surface-living Dreissena, show that the loss of pigmentation in this species is possibly the consequence of mutations in tyrosinase. This is important contribution to understanding the loss of pigmentation of subterranean animals outside the model organism – the Mexican tetra (Astyanax mexicanus).