On two new species of Nannopus Brady, 1880 (Copepoda: Harpacticoida: Nannopodidae) from intertidal mudflats of the Korean west coast (Yellow Sea).

Two new species in the genus Nannopus Brady, 1880 (Copepoda: Harpacticoida) from intertidal mudflats of the Yellow Sea along the Korean peninsula, Nannopus cylindricus sp. nov. and N. robustus sp. nov., are described. Nannopus cylindricus belongs to the group of Nannopus species with seven elements on P4 exp-3. Within this group, it is closest to a cryptic species complex related to N. ganghwaensis Vakati, Kihara Lee, 2016 based on an inflated caudal seta IV. However, N. cylindricus differs from the other species in this complex with respect to caudal seta V (inflated and heavily cylindrical at its base in N. cylindricus, inflated only in the N. ganghwaensis cryptic complex). Nannopus robustus belongs to the group of species displaying two setae on P2 enp-2. Within this group, N. robustus is closely related to N. serratus Vakati Lee, 2017 based on the presence of one endopodal naked seta arising from a stem-like protrusion on the mandibular palp. However, N. robustus can be distinguished from N. serratus based on the following characters: outermost distal spine on P2 exp-3 (extremely strong, smooth and recurved in N. robustus, moderately strong, denticulate and normal-shaped in N. serratus, and spine 1.6 times as long in N. robustus as in N. serratus), P2 exp-2 inner seta (absent in N. robustus, present in N. serratus), shape of caudal seta V (anterior part distinctly cylindrical in N. robustus, normal-shaped in N. serratus), and ornamentation of caudal seta VI (naked in N. robustus, pinnate in N. serratus). An updated key to the 17 valid species of Nannopus is provided.

Unraveling the intricate biodiversity of the benthic harpacticoid genus Nannopus (Copepoda, Harpacticoida, Nannopodidae) in Korean waters.

Nannopus (Harpacticoida, Nannopodidae) species are abundant and widely distributed throughout the world across a variety of habitats. Nannopus is well known for high frequencies of misidentifications and thus may comprise several cryptic complexes and morphologically distinct species. Cryptic taxa are common in meiofauna communities. In this study, we aimed to identify Nannopus species using an integrative approach including molecular taxonomy. We adopted a non-destructive DNA extraction method so that morphological and molecular data could be obtained from the same specimen. We analyzed the molecular diversity and distributions of Nannopus using a total of 190 individuals. We sequenced the 190 mtCOI, 53 mtCYTB, 25 18SrDNA, and 43 28SrDNA genes from 190 individuals. Several species delimitation approaches were applied, including uncorrected p-distances for mtCOI, mtCYTB, 18SrDNA, and 28SrDNA, and Automatic Barcode Gap Discovery and Bayesian implemented Poisson tree processes for mtCOI and mtCYTB data. The maximum likelihood and Bayesian approaches were used to examine the phylogenetic relationships among individuals using the combined set of all four genes. Our species delimitation and phylogenetic analyses indicated the presence of three cryptic and six morphologically distinct species. All species are sympatric and widely distributed across mudflats ranging from the Yellow Sea to the South Sea in Korea. The divergence patterns of the four genes were not congruent. A phylogenetic tree based on the concatenated dataset was the most robust, was congruent with morphology, and suggested two major clades. We considered the validity of reinstating the genus Ilyophilus (Lilljeborg, 1902) and ultimately concluded that including all congeners in Nannopus until the type species (N. palustris Brady, 1880) is re-described was the most prudent approach.

Five new species of the genus Nannopus (Copepoda: Harpacticoida: Nannopodidae) from intertidal mudflats of the Korean West Coast (Yellow Sea).

Five Nannopus Brady, 1880 species that are new to science are described from the intertidal mudflats of the Korean West Coast, Yellow Sea (South Korea). Nannopus minutus sp. nov. and N. dimorphicus sp. nov. belong to a group of species defined by seven elements on P4 exp-3, and these two species are unique by the pinnate caudal seta III. These species differ in the number of dorsal integumental windows on the cephalothorax (three in N. minutus, one in N. dimorphicus), shape of the distal small seta on the P4 endopod (naked in N. minutus, pinnate in N. dimorphicus), shape of the caudal seta IV (inflated and leaf-shaped in N. minutus, with a globular expansion at its insertion and slender in N. dimorphicus), and shape of the caudal seta V (anterior part cylindrical in N. minutus, inflated and bulbous in N. dimorphicus). The males of N. minutus and N. dimorphicus differ in the number of dorsal integumental windows on the cephalothorax (without any in N. minutus, with one integumental window in N. dimorphicus), number of outer spines on P2-P3 exp-3 (three in N. minutus, four in N. dimorphicus), shape of the inner seta on P3 enp-2 (naked in N. minutus, pinnate in N. dimorphicus), and shape of the outer medial and outermost setae on the P5 endopod (pinnate in N. minutus, naked in N. dimorphicus). Nannopus serratus sp. nov. and N. unisegmentatus Shen & Tai, 1964 share the presence of two setae on P2 enp-2 but differ in ornamentation and position of the setae on the mandibular palp, shape of the inner seta on P3 enp-2, and shape of distal seta on P4 enp-2. Nannopus parvus sp. nov. and N. bulbiseta sp. nov. belong to the group of species with the female P5 exopod fused, but these two species can be separated from the others by the presence of two bulbiform pinnate setae on the second segment of the antennule, as well as by the relative length and shape of the inner subdistal pectinate seta of P4 exp-3 (pectinate and 0.5 to 0.7 times as long as those in other congeners), and the shape of outer medial and outermost setae on the P5 endopod (naked only in female). However, they both display unique characters among all congeners. The caudal ramus of N. parvus is trapezoidal or square-shaped, and 0.4 to 0.5 times as long as those in other congeners, and the caudal seta V is very short and spine-like. Nannopus bulbiseta has four and five setae on P2 and P4 exp-3 respectively, the caudal ramus is sub-cylindrical or sub-rectangular, and the proximal part of the female caudal seta V is bulbous and very slender distally. A key to 14 valid species of Nannopus is provided.