Description of two deep-water copepods of the genus Leptotachidia Becker from the northwestern Pacific (Harpacticoida, Pseudotachidiidae)

Abstract. The monospecific genus Leptotachidia Becker, 1974 (Pseudotachidiidae Lang, 1936) was previously known only from the deep Atlantic. Female specimens of two unknown species of this genus were collected from abyssal sediments during an expedition to the northwestern Pacific on board research vessel ISABU (Korea Institute of Ocean Science and Technology) in November 2017. In this paper we describe the females of two new species, L. senariasp. nov. and L. apousiasp. nov. The new species were attributed to the genus Leptotachidia by the combination of the five-segmented female antennule, presence of the Brodskaya organ on the distal antennulary segment, and the second exopodal segments of second to fourth legs without inner setae. An outstanding character of both Pacific species is the reduced armature of thoracic legs in contrast to the type species, L. iberica Becker, 1974. In addition, the setal armature of L. senariasp. nov. and L. apousiasp. nov. is unique within the genus in that the female leg 5 of L. senariasp. nov. has six elements instead of five; and the antennary exopod of L. apousiasp. nov. bears a single seta on the proximal segment instead of two. This is the first record of Leptotachidia from the Pacific. A key to all three species of Leptotachidia is provided.