Descriptions of two deep-water copepods of the genus Leptotachidia Becker (Harpacticoida, Pseudotachidiidae) from the north-western Pacific

Abstract

The monospecific genus Leptotachidia Becker, 1974, belonging to the family Pseudotachidiidae Lang, 1936, was previously known from only the deep-sea of the Atlantic. During an expedition of the research vessel RV ISABU of the Korea Institute of Ocean Science and Technology (KIOST) in November 2017 from the north-western Pacific, second and third members of Leptotachidia were collected from abyssal sediments. The two new species, L. n. sp. 1 and L. n. sp. 2, are described herein based on the female specimens. They exhibit significant generic features: the female antennule five-segmented, with a Brodskaya organ on the distal segment and the second exopodal segment of second to fourth legs without inner setae. Outstanding character of both Pacific species is the reduced armature of thoracic legs in contrast to that of type species, L. iberica Becker, 1974. In addition, L. n. sp. 1 and L. n. sp. 2 have a unique setal armature in the genus such as the female P5 with six elements instead of five and the antennary exopod bearing a single seta instead of two on the proximal segment, respectively. This is the first record of Leptotachidia species in the Pacific and a key to the species ofLeptotachidia is provided.