A revision of the family Archinotodelphyidae Lang, 1949 (Copepoda: Cyclopoida Oithonida), with the recognition of 15 new species Author Kim, Il-Hoi Korea Institute of Coastal Ecology, Inc., 802 - ho, 302 - dong, 397 Seokcheon-ro, Ojeong-gu, Bucheon, Gyeonggi-do 14449, Republic of Korea Author Boxshall, Geoff A. Department of Life Sciences, Natural History Museum, Cromwell Road, London SW 7 5 BD, United Kingdom g. boxshall @ nhm. ac. uk; https: // orcid. org / 0000 - 0001 - 8170 - 7734 text Zootaxa 2020 2020-06-17 4801 1 1 56 journal article 10.11646/zootaxa.4801.1.1 1175-5326 3898064 74E0BE48-4E84-4EC5-9360-3021F2756AF7 Archinotodelphys unisetosus sp. nov. (Figs. 32, 33) Type material. Holotype ( ♀ , MNHN-IU-2014-21211, dissected and mounted on a slide). Type host. unidentified Phlébobranche. Type locality. North Atlantic , ABYPLAINE cruise, N/0 Cryos , Stn DS 11, 42°59.7´N , 14°05.4´W , depth 5260 m , Monniot coll., 12-13 June 1981 . Etymology. This name of the species alludes to the presence of a single seta only on the first endopodal segment of the mandible, a unique character state for the family. Female. Body (Fig. 32A) small, length 815 μm: prosome 495 μm long; greatest width 298 μm across cephalo- some. Urosome (Fig. 32B) 5-segmented; fifth pedigerous somite 107 μm wide. Genital double-somite almost as long as wide (104×100 μm); paired genital apertures located dorsolaterally at 40% of double-somite length. Three free abdominal somites 45×72, 44×71, and 45×73 μm, respectively. Caudal rami separated from each other; each ramus (Fig. 32C) about 2.6 times longer than wide (67×26 μm), armed with 6 setae, all pinnate; outer lateral seta located at 38% of ramus length. Rostrum (Fig. 32D) triangular, 51×42 μm. Antennule (Fig. 32E) 202 μm long and 12-segmented; armature formula 3, 5, 7, 2, 2, 6, 4+aesthetasc, 4, 2+aesthetasc, 2, 2 + aesthetasc, and 7+aesthetasc; all setae naked. Antenna (Fig. 32F) with unarmed coxa; basis with 2 subequal exopodal setae at outer distal corner; endopod 3-segmented with 1, 4, and 6+claw on first to third segments, respectively; terminal segment 2.3 times longer than wide. Labrum (Fig. 32G) with large posteromedian lobe and setulose distal margin. Mandible (Fig. 32H) with 2 teeth and 2 setae on coxal gnathobase; basis with 1 seta on medial margin; exopod 4-segmented, each segment with 1 seta; endopod with 1 and 7 setae on first and second segments. Maxillule (Fig. 32I) with 9 setae on precoxal arthrite; coxa with 1 seta on endite and 2 setae on epipodite; basis with 6 setae on medial margin; exopod with 4 setae distally; endopod with 5 setae, 3 medial and 2 distal. Maxilla (Fig. 33A) 5-segmented; syncoxa with 4 (including 1 small), 1, 2, and 3 setae on first to fourth endites; basis with 1 smooth claw and 2 setae; endopod 3-segmented with 1, 2, and 3 setae on first to third segments, respectively. Maxilliped (Fig. 32J) 3-segmented with 4 (1, 1, and 2), 1, and 3 setae on first to third segments, respectively. Legs 1–4 biramous with 3-segmented rami (Figs. 33B-D); armature formula for legs 1–4 as generic diagnosis. All setae on legs pinnate. Inner distal spine on basis of leg 1 (Fig. 33B) 33 μm long, longer than first endopodal segment, proximally pinnate but distally spinulose. Leg 5 (Fig. 33E) protopodal segment wider than long, probably with 1 outer seta (detached but attachment scar discernible); exopodal segment about 1.9 times longer than wide (50×26 μm), with 3 large, pinnate setae and 1 smaller, naked seta. Leg 6 (Fig. 33G) represented by 1 spine and 1 seta on genital operculum. Male. Unknown. Remarks. This deep-water species exhibits extreme reduction of the mandibular endopod with the fewest setae of any known species: 1 on the first segment and 7 on the second. In other species the first segment is armed with between 4 and 6 setae, and the second segment between 8 and 10 setae. The antennule of the female is 12-segmented in A. unisetosus sp. nov. , which is another unique character state. Most other species have more expressed segments (14 to 17) and only A. profundus has fewer, with only 10 (cf. Huys & Boxshall, 1991 : Fig. 2.8.9A). The maxillule has only 5 setae on the endopod in A. unisetosus sp. nov. This compares with 8 to 11 in all other species except A. polynesiensis and A. phallusiae comb. nov . , each of which apparently has 12 setae ( Hansen, 1923 ), although these counts require confirmation as 12 is more than is found in any other known member of the order Cyclopoida ( Huys & Boxshall, 1991 ) . This is the deepest known record of any described species of Archinotodelphyidae but the family inhabits considerably deeper waters. Khodami et al . (2019) sequenced unidentified archinotodelphyids collected from depths of 8734 to 9013 m at the Kuril Trench in the North Pacific.