Abstract <p>Problematic Hydroidea of the genus Fistulella were found in ore-bearing rocks of the Saf’yanovo massive sulfide copper–zinc deposit. The systematic position of this genus has not been determined. Fistulella, classified as problematic Hydroidea in (Shuysky, 1970), resemble the algae-type tubular organisms. They are reef builders and quite common in Paleozoic reefs of the northern Urals, where they form a type of biohermal limestones in association with algae, in particular, <i>Ikella vermicularis</i> (Shuysky, 1970). The ore-hosting sequence of the Saf’yanovo deposit includes the Silurian (Przhidolian) volcanic rocks. Attenuation of reef formation was noted at the Przhidolian stage in the northern Urals. Predominantly autotrophic communities of reef structures (small banks and bioherms) are replaced by heterotrophic communities (including problematic Hydroidea), characterizing the shoal conditions of the open sea. Findings of the remains of problematic organisms of the genus Fistulella at the Saf’yanov deposit are of great importance, because they suggest that the ore-hosting sequence in the deposit, along with volcanic rocks and sedimentary carbonaceous–siliceous rocks, also includes the remains of biohermal buildups and indicates a shallow sedimentation environment. The buildups were probably pre-ore structures, because the detected organism remains were replaced by carbonates of the magnesite–siderite series.</p>