Does salinity make a difference—Kidney anatomy of Saimaa ( <i>Pusa saimensis</i> ) and Baltic ringed seals ( <i>Pusa hispida botnica</i> )

As habitat salinity markedly differs between the endangered, freshwater-dwelling Saimaa ringed seal (Pusa saimensis Nordquist, 1899) and the brackish water-inhabiting Baltic ringed seal (Pusa hispida botnica Gmelin, 1788), we investigated whether this difference has resulted in morphological changes to their kidneys. We studied kidney anatomy using dissection, silicone casts, and standard histological methods. The Saimaa ringed seal had statistically significantly fewer reniculi than the Baltic ringed seal, and the mean number of reniculi was significantly smaller in both studied species than that previously reported from Arctic ringed seals (Pusa hispida hispida Schreber, 1775). We described four of the most common branching patterns of the renal artery. Contrary to previous findings in other ringed seal studies, we observed veins resembling arcuate and interlobar veins in histological sections of both species.