Phestilla subodiosus sp. nov. (Nudibranchia, Trinchesiidae), a corallivorous pest species in the aquarium trade.

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 lade with Phestilla. Based upon a literature review, its original morphological description, and our phylogenetic hypothesis, we reclassified this species as Phestilla chaetoptemna comb. nov.