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.
Highlights
Despite their abundance and high biomass in deep-sea meiobenthic assemblages, little is known on the diversity of abyssal harpacticoids and more than 95% of them remain undescribed (Seifried 2004)
The presence of aesthetascs on the mouthparts, which character is unique within other harpacticoid families and its position is homologous, is a significant synapomorphy for a core of genera, Jonesiella Brady, 1880, Paradanielssenia Soyer, 1970, Leptotachidia Becker, 1974, Micropsammis Gee & Huys, 1991, Telopsammis Gee & Huys, 1991, Peltisenia Huys & Gee, 1996, Sentiropsis Huys & Gee, 1996, and Nyxis Willen, 2009 (Gee and Huys 1991; Willen 2005, 2008, 2009; Willen and Schulz 2007; Kim et al 2011)
The danielsseniin Paradanielssenia group composed of Paradanielssenia, Leptotachidia, Micropsammis and Telopsammis shares the aesthetascs on the mouthparts modified into claviform stuructures (Gee and Huys 1991; Willen 2008, 2009)
Summary
Despite their abundance and high biomass in deep-sea meiobenthic assemblages, little is known on the diversity of abyssal harpacticoids and more than 95% of them remain undescribed (Seifried 2004). Most taxonomic studies on abyssal harpacticoids have been performed in the Atlantic (Seifried 2004) and a limited number of papers are available on the deep-sea harpacticoid fauna from the Pacific (e.g. Itô 1982, 1983; Humes and Voight 1997; Huys and Conroy-Dalton 1997; Lee and Yoo 1998; ConroyDalton and Huys 1999, 2000; Lee and Huys 1999, 2000; López-González et al 2000; Gollner et al 2008; Back et al 2010; Cho et al 2016; Gómez and Díaz 2017; Vakati et al 2017; Gómez 2018a-c; George and Schwabe 2019). A key to species of the genus is given This is the first record of Leptotachidia from the Pacific
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