Tracking blind journey in the deep-sea: origin and evolutionary history of the Typhlotanaidae (Crustacea: Tanaidacea)

The Typhlotanaidae are regeared as one of the most diverse families within the suborder Tanaidomorpha; their actual diversity and evolutionary history remain poorly understood. To elucidate the evolutionary history within this group, we analysed three molecular markers, i.e., the mitochondrial cytochrome oxidase I (COI), the nuclear 18S rRNA, and histone 3 (H3) gene. This represents the first phylogenetic investigation of the family Typhlotanaidae and, more broadly, the first molecular attempt to reconstruct evolutionary relationships within the suborder Tanaidomorpha. The phylogenetic reconstruction revealed the polyphyletic nature of the Typhlotanaidae, leading to elevation to the two genera of the family rank. Furthermore, by applying an integrative approach that combined molecular and morphological evidence, three new typhlotanaid subfamilies were defined, one subfamily was re-established, and two new genera were erected. The number of species included in the Typhlotanaidae has considerably reduced, with the family now comprising 119 valid species. • First phylogenetic reconstruction of the deep-sea family Typhlotanaidae based on three molecular markers (COI, 18S rRNA, H3). • Integrative taxonomy combining morphology and molecular data reveals the polyphyly of Typhlotanaidae. • Two problematic genera ( Meromonakantha and Paratyphlotanais ) are reassigned and formally elevated to new families: Meromonakanthidae fam. nov. and Paratyphlotanaidae fam. nov. • Three new subfamilies (Proctagoninae, Starkinae, Typhlaminae) are established and one redefined (Typhlotanainae). • Revised taxonomy reduces the number of valid Typhlotanaidae species to 119, providing a new evolutionary framework for Tanaidomorpha.