Species boundaries and phylogeographic patterns in new species of Nannoniscus (Janiroidea: Nannoniscidae) from the equatorial Pacific nodule province inferred from mtDNA and morphology

Abstract Spatial patterns of genetic variation (based on COI and 16S mtDNA) for morphologically similar species in the isopod genus Nannoniscus G.O. Sars. 1870 were examined that occur broadly across the Clarion Clipperton Fracture Zone (CCZ). Samples were obtained from five different licence areas as well as an Area of Particular Environmental Interest (APEI-6) with sites located at various distances (a few to several hundred kilometres) from one another. Applying three different species delimitation (SD) methods (sGMYC, mPTP and ABGD) of the molecular data, we could distinguish between four and 12 different molecular taxonomic operational units (MOTUs). Morphological analyses could confirm five distinct phenotypic clades that represent species new to science and are described here: Nannoniscus brenkei sp. nov., Nannoniscus hilario sp. nov., Nannoniscus magdae sp. nov., Nannoniscus menoti sp. nov. and Nannoniscus pedro sp. nov. Despite the assumed limited dispersal capacity of Nannoniscus species, we found haplotypes of two species to be geographically widespread (up to > 1400 km apart), as opposed to several divergent clades occurring in close vicinity or even sympatry. Geographic distance appeared to explain the phylogeographic structure of Nannoniscus species to some extent, although oceanographic features and level of environmental heterogeneity were probably equally important.