Decoding the evolutionary history and systematic complexity of Pseudotanaidae (Crustacea: Tanaidacea)

The family Pseudotanaidae (Tanaidacea) comprises ecologically significant deep-sea crustacean taxa, yet its phylogenetic relationships remain poorly resolved due to limited molecular data. This study integrates targeted sequencing (COI, 18S) and mitogenomic analyses to reconstruct the evolutionary history of Pseudotanaidae. Phylogenetic trees inferred using Maximum Likelihood (ML) confirm the monophyly of the family while revealing polyphyly within the genus Pseudotanais. Genetic divergence among sampled individuals corresponds closely with morphological groupings, indicating the presence of distinct evolutionary lineages. Our study significantly expands the molecular dataset for Pseudotanaidae, increasing the number of COI and 18S sequences in public databases more than twentyfold. Furthermore, we present the first mitogenomes of deep-sea tanaids, revealing unique mitochondrial features. Notably they all feature an unexpected reassignment of the TAA stop codon to tyrosine, in the otherwise typical invertebrate mitochondrial translation table. These findings establish a robust framework for future taxonomic and evolutionary studies, emphasizing the need for expanded genomic sampling to resolve remaining uncertainties in Pseudotanaidae phylogeny.