Phestilla subodiosus sp. nov. ( Nudibranchia : Trinchesiidae ) is a novel species that feeds on corals in the genus Montipora ( Scleractinia : Acroporidae ) which are economically important in the aquarium industry. Nuclear-encoded H3, 28SC1-C2, and mitochondrial-encoded COI and 16S markers were sequenced. Phylogenetic analysis, Automatic Barcode Gap Discovery (ABGD), morphological data, and feeding specialization all support the designation of Phestilla subodiosus sp. nov. as a distinct species. Although new to science, Phestilla subodiosus sp. nov. had been extensively reported by aquarium hobbyists as a prolific pest over the past two decades. The species fell into a well-studied genus, which could facilitate research into its control in reef aquaria. Our phylogenetic analysis also revealed Tenellia chaetopterana formed a well-supported clade with Phestilla . Based upon a literature review, its original morphological description, and our phylogenetic hypothesis, we reclassified this species as Phestilla chaetopterana comb. nov.