Second members of the harpacticoid genera Pontopolites and Pseudoleptomesochra (Crustacea, Copepoda) are new species from Korean marine interstitial

摘要

Monotypic genera present a specific set of problems in phylogenetic analyses, and their familiar placements are often provisional. Our survey of Korean copepods in marginal habitats resulted in a discovery of two new species, both representing second members of their respective genera: Pontopolites duljjae sp. nov. and Pseudoleptomesochra mannada sp. nov. This gave us an opportunity to contribute a set of novel characters, including previously unused cuticular organs on somites, and to evaluate the most important synapomorphies in each genus. Pontopolites duljjae differs from the northern Atlantic Pontopolites typicus Scott T., 1894 in the segmentation of antennula and armature of several appendages. Especially intriguing is the sexual dimorphism in the segmentation and armature of the second to fourth leg endopods, but this is probably a plesiomorphic character state in a larger group of nannopodids. We provide an amended diagnosis of the genus Pontopolites Scott T., 1894. In contrast, morphological differences between our Psudoleptomesochra mannada and its congener from the northeast Pacific, Psudoleptomesochra typica Lang, 1965, are rather minute and contribute very little to the generic diagnosis. In both new species, cuticular organs show very little intraspecific variability and sexual dimorphism, which provides an invaluable tool for matching females and males in samples from different localities or sympatric congeners, as well as for delimitation of closely related species using cuticular organs as landmarks for geometric morphometric analyses. They can also be useful characters for reconstructing phylogenetic relationships, especially in interstitial groups with numerous appendage reductions, such as members of Nannopodidae and Ameiridae.