Shortly before the mass mortality event of the noble pen shell ( ) population in the south-eastern Adriatic coast, two rapidly growing strains CVI_P3 (DSM 114013 T, ATCC TSD-295 T) and CVI_P4 were obtained from the organs of individual mollusks during the regular health status monitoring. The strains were identified as members of the genus using basic phenotypic characteristics, genus-specific PCR assays targeting the and 16S rRNA genes and the commercial hybridization kit GenoType Mycobacterium CM (Hain Lifescience, Germany). MALDI-TOF mass spectrometry did not provide reliable identification using the Bruker Biotyper Database. Genome-wide phylogeny and average nucleotide identity (ANI) values confirmed that the studied strains are clearly differentiated from their closest phylogenetic relative and other validly published species (ANI ≤ 85.0%). The type strain CVI_P3 was further characterized by a polyphasic approach using both phenotypic and genotypic methods. Based on the phenotypic, chemotaxonomic and phylogenetic results, we conclude that strains CVI_P3 and CVI_P4 represent a novel species, for which the name sp. nov. is proposed.