Atlantapseudes tridens Matsushima, Bâlcu & Kakui, 2025, sp. nov.

Atlantapseudes tridens sp. nov. [New Japanese name: Sanbonduno-apuseudesu] (Figs 5–8) Atlantapseudes sp.: Kakui et al. 2011, table 1, figs 2–5; Matsushima & Kakui 2024, fig. 7. Type material. Holotype: preparatory female (ICHUM4002, TBL = 7.10 mm, CW = 1.39 mm, 11 slides and one vial), R/V Soyo-maru, Stn Kago-7, Okinawa Trough, East China Sea (28°29'24.0"N, 127°59'30.0"E to 28°29'42.0"N, 128°00'48.0"E), 1076–1079 m depth, plankton net attached inside beam trawl, 29 July 2010, collected by K. Kakui. Paratype: one preparatory female (ICHUM8985, TBL = 5.66 mm, CW = 1.05 mm, 11 slides and one vial, R/V Soyo-maru, Stn Kago-9, Okinawa Trough, East China Sea (27°30'27.5"N, 126°58'10.9"E to 27°30'47.8"N, 126°58'04.0"E), 1595– 1557 m depth, plankton net attached inside beam trawl, 26 July 2014, collected by K. Kakui. Representative DNA Sequences. One 18S (INSD accession number AB618176; 2189 bp long; Kakui et al. 2011) and one COI (LC860315; 658 bp long, encoding 219 amino acids; this study) sequences were determined from the holotype. Etymology. The specific name tridens (Latin: trident) is a noun in the nominative case, referring to the shape of the tridentate rostrum. Diagnosis. Rostrum tridentate. Epistome strongly curved ventrally. Pereonites 1 and 2 without lateral spines. Lateral margin of pereonites 3–6 with anterior spine (tiny in pereonite-6) but without posterior spines. Squama more than twice longer than antennal article-3. Labial palp with two distal spiniform setae. Maxillipedal palp article-2 with outer distal seta. Chelipedal carpus with two ventral long setae. Description of female (based on holotype unless noted otherwise). Body (Figs 5, 6A 1, 2, B [holotype ICHUM4002]; 6C1–4, D [paratype ICHUM 8985]) well calcified, dorsoventrally flattened, 5.1 times longer than CW, whitish in specimens before fixation (Fig. 5). Cephalothorax length 0.2 times TBL, 1.1 times as long as wide; rostrum tridentate; eye lobes distinct, with anterior spine; mid-lateral margin with spine; acute ventral keel (hyposphenium) present, posterior to maxillipeds. Epistome (Fig. 6E) strongly curved ventrally. Pereonites 1–6 with length ratio 1.00: 1.16: 1.59: 1.84: 1.79: 1.25; with width/length ratio 3.09: 2.31: 1.93: 1.89: 1.59: 1.70 and with acute hyposphenium; lateral margin of pereonites 3–6 with anterior spine, with the spine of pereonite-6 tiny. Pleon length 0.2 times TBL. Pleonites distinctly narrower than pereonites; each pleonite with width/length ratio 3.60: 3.01: 3.05: 3.06: 2.48, similar in shape, with hyposphenium (acute in holotype; obtuse and rounded on pleonites 1–4 but acute on pleonite- 5 in paratype; Fig. 6B, D); epimera (Fig. 6A 2, B, C 4, D) projecting ventroposteriorly, with pointed apex. Pleotelson (Fig. 6A 2, B, C 4, D) 1.1 times as long as wide, narrower than pleonites, with posterior projection. Antennule (Fig. 7A) with eight-articled outer flagellum and three-articled inner flagellum. Combined length of peduncle and outer flagellum 1.26 times longer than cephalothorax. Peduncular articles 1–4 with length ratio 1.00: 0.41: 0.11: 0.11; article-1 with two mid-outer, one mid-inner, and one inner subdistal simple setae and ten outer (four broken) PSS; article-2 with one mid-outer, two outer distal (one long), one inner subproximal, and one inner subdistal simple setae and three outer distal (one broken) and two inner distal PSS; article-3 with one outer distal and three inner distal simple setae; article-4 with two PSS at insertion of outer flagellum. Outer flagellum 0.5 times as long as peduncle; articles 1 and 2 naked; articles 3–8 with three distal, one distal, three distal (one long), one distal, two distal (one long), and two middle and four distal simple setae, respectively; article-8 with one PSS (broken); article-7 with distal long aesthetasc. Inner flagellum 0.5 as long as outer flagellum; articles 1–3 with two, one (broken), and three (one broken) distal simple setae, respectively; articles 1–3 each with distal PSS. Antenna (Fig. 7B) with 11 articles, 0.9 times as long as antennule; articles 1–11 with length ratio 1.00: 1.80: 0.67: 1.56: 2.43: 0.91: 0.64: 0.63: 0.46: 0.47: 0.45. Article-1 naked. Article-2 with one outer subproximal, one outer distal, and one inner subproximal simple setae. Article-3 with inner distal simple seta. Article-4 with inner subproximal simple seta and two inner subdistal PSS (one broken). Article-5 with one inner subproximal and one inner subdistal simple setae and one outer subproximal, one mid-outer, two inner subdistal, and two dorsal subdistal PSS. Article-6 with one mid-outer, one distal long, and one inner subdistal simple setae. Articles 7–11 with three distal (one long), one inner subdistal and three distal (one long, one broken), two distal (one long, one broken), and five distal simple setae, respectively; article-9 with inner distal PSS. Squama 0.2 as long as antenna, 2.4 times longer than antennal article-3, and 1.0 times as long as antennal article-4; narrow, with two simple setae (one long). Labrum (Fig. 7C) bipartite with numerous fine setae. Mandibles (Fig. 7D–G) with well-developed molar process bearing six tufts of fine setae (Fig. 7D). Left mandibular incisor (Fig. 7E) with five rounded processes; setiferous lobe with two setulate and serrate setae, two setulate bifurcate setae, two spiniform setae, and fine setae; lacinia mobilis with five rounded processes. Right mandibular incisor (Fig. 7F) with four rounded processes; setiferous lobe with five round-tipped setae and fine setae. Palp (Fig. 7G) with three articles; articles 1–3 with length ratio 1.00: 2.67: 0.79; article-1 with middle simple seta; article-2 with seven bipinnate setae in distal region; article-3 with 10 distal bipinnate setae. Labium (Fig. 7H) with lobe bearing several outer simple setae and inner setation. Palp with several short and long simple setae on lateral margins, and two distal bifurcate spiniform setae. Maxillule (Fig. 7I) with biarticulate palp; palp article-1 with three fine setae; palp article-2 with five pinnatetipped setae (one broken) in distal half. Outer endite with numerous simple setae in middle region, outer proximal and inner fine setation, 10 distal spiniform setae, and two subdistal plumose setae. Inner endite with outer and inner distal fine setation and three distal setulate spiniform setae. Maxilla (Fig. 7J) with body bearing inner distal fine setae, short simple setae in inner distal region, 13 outer distal simple setae, and outer proximal serration. Inner lobe of fixed endite with several short simple setae, three biserrate setae, and 17 basally swollen setae. Outer lobe of fixed endite with outer fine setae, eight inner short simple setae, six distal simple setae, one distal and one subdistal plumose setae, and three distal trifurcate setae. Inner lobe of movable endite with inner fine setae, nine ventral short simple setae, three plumose setae (one broken), furcate seta, and four distal simple setae. Outer lobe of movable endite with two ventral short simple setae and seven setulate serrate setae. Maxilliped (Fig. 7L, l 1, K) with naked coxa. Basis with outer fine setae and two mid-inner simple setae. Endite (Fig. 7K, paratype) with several fine setae in middle region; inner region with four setulate serrate setae and two coupling hooks; distal region with fine setae, two plumose setae, and eight setulate serrate setae. Palp article-1 with one outer distal seta and one inner distal simple seta; article-2 with one outer distal and eleven inner simple setae; article-3 with eleven inner simple setae; article-4 with nine inner simple setae and two inner serrate setae (broken) (Fig. 7l 1). Epignath (Fig. 7M, paratype) cup-shaped, with setulate terminal seta. Cheliped (Fig. 8A) without exopod. Basis 2.6 times as long as wide, with one mid-dorsal and four ventral simple setae and one dorsoproximal and one ventro-subdistal spines; inner surface smooth. Merus with ventrodistal simple seta and ventrodistal spine. Carpus 0.64 times as long as basis, 2.5 times as long as wide, with one dorso-subproximal, one dorsodistal, two ventro-subdistal short simple setae and two ventral long simple setae. Propodus with one mid-outer and four ventral simple setae; dorsal region of palm with two distal simple setae; cutting surface with one outer proximal, two inner proximal, and two inner subdistal simple setae, eleven outer round-tipped setae, and several denticles; unguis curved and pointed. Dactylus longer than fixed finger, with three outer and three inner simple setae and several denticles; unguis curved and pointed, longer than fixed-finger unguis. Pereopods 1–6 with length ratio 1.00: 0.94: 0.82: 0.84: 0.88: 0.82. Pereopod-1 (Fig. 8B) 0.5 times as long as TBL, with length ratio of basis, ischium, merus, carpus, propodus, and dactylus–unguis 1.00: 0.07: 0.43: 0.39: 0.28: 0.27. Coxa with anterior spine and six plumose setae. Basis 4.83 times as long as wide, with one dorso-subdistal, one mid-ventral, one ventro-subdistal, and two ventrodistal (one broken) simple setae and two mid-dorsal (one long) PSS. Ischium with two ventrodistal simple setae. Merus with ventro-subproximal row of five simple setae, four dorsodistal and three ventrodistal simple setae, and ventrodistal spiniform seta. Carpus with two mid-dorsal, six dorsodistal, four ventral, and three ventrodistal simple setae and one dorsodistal and two ventrodistal spiniform setae. Propodus with one mid-dorsal, one dorsodistal, and two ventrodistal simple setae, two dorsal and five ventral spiniform setae, inner dorso-subdistal PSS, and inner ventrodistal pinnate seta. Dactylus with two dorso-subproximal simple setae and three ventral spines; unguis half as long as dactylus, naked. Pereopod-2 (Figs. 6A 1, B, C1, D, 8C) with length ratio of articles from basis to dactylus–unguis 1.00: 0.13: 0.36: 0.38: 0.32: 0.34. Coxa with spine (broken in left pereopod-2 of holotype, Figs. 6A 1, B, C1, D) and three small simple setae. B