Hidden diversity in the deep North Pacific and Atlantic: New taxa and a revised subfamilial framework of Akanthophoreidae (Crustacea: Tanaidacea)

• Integrative taxonomy reveals hidden diversity in deep-sea Akanthophoreidae. • Monophyly of the family confirmed using morphology and 18S rRNA data. • Three distinct subfamilies defined: Akanthophoreinae, Chauliopleoninae, and Stenotanainae. • Two new Stenotanais species and a new genus, Bamberotanais , described. • Findings suggest inter-basin connectivity of deep-sea tanaidaceans. Tanaidaceans of the family Akanthophoreidae are a morphologically diverse group of peracarid crustaceans inhabiting deep-sea environments. However, their true diversity and evolutionary relationships remain poorly resolved. In this study, we examine material collected from the North Pacific and Atlantic Oceans to investigate the phylogenetic structure of Akanthophoreidae using morphological data and 18S rRNA gene sequences. Our results confirm the monophyly of the family and support its subdivision into three morphologically and genetically distinct subfamilies: Akanthophoreinae Sieg, 1986 , Chauliopleoninae subfam. nov., and Stenotanainae subfam. nov. We provide formal diagnoses for each subfamily and revise the genus Stenotanais, describing two new species from the North Pacific. In addition, we establish Bamberotanais gen. nov. to accommodate four new species. Species of Stenotanainae were collected from depths ranging from 805 to 5740 m across the Clarion-Clipperton Zone, Kuril-Kamchatka and Aleutian Trenches, and the northwest Atlantic margin. The discovery of Stenotanainae in both the Pacific and Atlantic extends the known distribution of this group and suggests greater inter-basin connectivity than previously assumed. In total, the number of recognised species in Akanthophoreidae increases from 56 to 62, and the number of genera from ten to eleven. This study highlights the utility of integrative taxonomy in uncovering hidden deep-sea biodiversity and provides a revised phylogenetic framework for future research on the evolutionary history of Tanaidacea.