Five new species of Tetragoniceps Brady, 1880 (Copepoda, Harpacticoida, Tetragonicipitidae) from Korea

Five new species of the genus Tetragoniceps Brady, 1880, collected from Korean waters, are described. These new species are readily distinguished from other congeners by a unique armature formula of legs 2–4, notably with one inner seta on the two proximal exopodal segments, and six, five, and seven elements on the distal exopodal segments of legs 2–4, respectively, a combination not previously reported in Tetragoniceps.

Additional specific diagnostic features of the five new species include the shape and length of the caudal rami, the morphology of leg 5, relative lengths of the inner setae on exopods of legs 2–4, setation of the mandibular exopod, maxillular exopod, and distal endopod segment of leg 1, and sexually dimorphic features of the middle exopodal segment of leg 4 in the male. A comparative table for all known Tetragoniceps species, incorporating revised interpretations of several diagnostic characters including the armature formula for the distal exopodal segment of leg 4 in the female, is provided, together with an updated identification key.

This study represents the first record of Tetragoniceps from the northwestern Pacific, substantially expanding the known geographic distribution of the genus.