This paper is a first detailed contribution to the knowledge of serpulid diversity from marine caves of the eastern Mediterranean Sea. A total of 27 taxa were recorded in two submerged caves of Lesvos Island, in the Aegean Sea. A clear trend of variability was observed with serpulid abundance, specifically that of sciaphilic and deep-sea species, increasing inwards while the number of taxa and species diversity did not change significantly across the two caves. In the innermost sectors of the studied caves two types of bioconstructions were observed: (a) ‘coiled doughnuts’ of Protula, recorded for the first time in Mediterranean caves; and (b) ‘biostalactites’ mainly consisting of skeletal metazoans recorded for the first time from the eastern Mediterranean. The results of the present study revealed new faunal elements and type of bioconstructions for the Mediterranean marine caves, showing that several aspects of their communities are still poorly known and deserve to be further investigated.