Description of a novel Ligia species from Nihoa, a remote island in the Papahānaumokuākea Marine National Monument.

Isopods in the genus Ligia have been shown to harbor deeply divergent genetic lineages that have, in some instances, been recognized as cryptic species. For instance, the use of molecular taxonomic approaches to characterize coastal Ligia from the Hawaiian Islands led to the redescription of Ligia hawaiensis, the sole endemic coastal species previously recognized in the region, and to the description of seven new species endemic to the region. These species appear to be highly restricted to rift zones within single islands, single islands, or previously connected islands, suggesting these species evolved in allopatry. These findings, coupled with the poor dispersal capabilities exhibited by Ligia isopods and the geology of the Hawaiian Islands, suggest that additional cryptic species may exist in highly isolated populations yet to be studied. Studies to date have characterized Ligia from throughout the younger Hawaiian Islands (e.g., Kaua' i, O' ahu, Moloka' i, Maui, Lanai, and Hawai' i); however, no endemic Ligia populations from the older islands and more remote islands that form part of the Papahānaumokuākea Marine National Monument (PMNM) have been studied. This region represents the largest marine conservation area in the USA, and includes at least three islands where L. hawaiensis have been previously reported from. Herein, we apply molecular taxonomic approaches to characterize Ligia specimens from Nihoa, a remote island in the PMNM. Results show that Ligia from Nihoa form a highly divergent that is reciprocally monophyletic lineage with other Hawaiian Ligia species. This lineage, described as Ligia barack sp. nov., adds to the known biodiversity of the PMNM and highlights the importance of continued exploration and conservation of this remote and highly biodiverse region.