The Paralicella Paradox: Broadly Distributed Lineages Without Clear Geographic Partitioning in Paralicella tenuipes and the Paralicella caperesca Species Complex

Abyssal environments (3000–6000 m ocean depth) are often presumed to promote broad genetic connectivity across ocean basins due to their vast spatial extent, apparent environmental homogeneity and few barriers to gene flow. While some deep‐sea taxa conform to this expectation, growing evidence shows that marked genetic structure can persist even in widely distributed species. Here, we reassess lineage structure within two widespread abyssal amphipods, Paralicella tenuipes Chevreux, 1908 and Paralicella caperesca Schulenberger & Barnard, 1976, using multilocus data (COI, 16S rRNA, 28S rRNA) from expanded global abyssal sampling. Species delimitation analyses recovered recurrent mitochondrial lineage structure within P. tenuipes and stronger multilocus divergence within P. caperesca , consistent with interpretation of the latter as a species complex. TCS haplotype networks showed no consistent geographic or depth‐associated separation, with recovered lineages and major haplotypes distributed across multiple ocean basins. Demographic and neutrality tests indicated moderate to high mitochondrial diversity in P. tenuipes but no consistent species‐wide signal of recent demographic change, whereas P. caperesca showed higher mitochondrial diversity and stronger, marker‐dependent demographic signals. Together, these results indicate genetic structure that is not strongly associated with geography or depth. The geographic extent of sampling demonstrates that Paralicella ranks among the most widely distributed deep‐sea amphipod genera to date. This combination of broad abyssal distribution and non‐geographically associated lineage structure indicates that the processes generating genetic diversity in these amphipods do not align neatly with the geographic units commonly used to infer diversification in abyssal ecosystems.