Haploniscus apaticus Knauber & Riehl 2025, sp. nov.

Haploniscus apaticus Knauber & Riehl sp. nov. Figs 6, 7, 8, 9, 26 Holotype. SKB Hap 08, adult male (stage VI), 3.3 mm, MIMB 50307. Paratypes. SKB Hap 18, adult female (stage IV), 3.2 mm, MIMB 50308; SKB Hap 48, adult female (stage IV; genome), SMF 56565. Type locality. St. LV 71–04 – 10, RV “ Akademik M. A. Lavrentyev ”, SokhoBio expedition, EBS, 3366 m, 47°12.2'N, 149°36.7'E, Northwest Pacific, Sea of Okhotsk, Kuril Basin. Further records. St. LV 71–02 – 07: SKB Hap 27 (manca) SMF 56544, SKB Hap 36 (manca) MIMB 50309; St. LV 71–04 – 09: SKB Hap 55 (manca) MIMB 50310, SKB Hap 62 (adult male) SMF 56579; St. LV 71–10 – 07: SKB Hap 02 (adult female) SMF 56519. Distribution. Northwest Pacific, Sea of Okhotsk, Kuril Basin, depth 3351–3366 m. Visualized in Fig. 27. Etymology. “ apaticus ” is a Latinized adjective derived from “ Apate ”, the goddess of deceit in Greek mythology. This name refers to this species’ lack of a pronounced sexual dimorphism, e. g., in the pleotelson shape, and overall inconspicuous morphology, keeping it hidden amongst its sibling species until recently. Haploniscus apaticus can be interpreted in English as “ deceitful or deceptive Haploniscus. ” Synonymy. Haploniscus SO - SO (see Knauber et al. 2022). Diagnosis. Differs from other species of the belyaevi - complex in the following characters: Prn 4 lateral margin longer than Prn 5 lateral margin; Plt posterolateral processes straight, oriented posterolaterally; PV – VII lengths distinctly exceeding PI – IV lengths. Molecular diagnosis. differing in the COI gene from other species of the belyaevi - complex in the nucleotides T (position 69 of the alignment), A (220), A (364), G (412), G (469), A (475), and C (556). Description. Male. Body (Fig. 6 B) length 2.5 width; oval; anterior body length (Ceph – Prn 4) 1.0 posterior body length (Prn 5 – Plt); lateral margin interrupted between Prn 7 and Plt, otherwise continuous. Cephalothorax (Fig. 6 B, D) length 0.41 width, 0.10 body length, width 0.59 body width; frontal margin width 0.48 Ceph width; rostrum curved upwards. Pereonite 1 (Fig. 6 B) posterior tergite margin through Prn 5 anterior tergite margin delicately serrated, setose; Prn 2–5 anterolateral angles slightly projecting; Prn 1–4 posterolateral angles slightly projecting; Prn 4 lateral margin length 1.17 Prn 5 lateral margin length. Pleotelson (Figs 6 B, 26 J) length 0.79 width, 0.25 body length, trapezoidal, posterior margin rounded, convex; tergite surface smooth; with posterolateral tergal ridge between uropod insertion and posterolateral process; posterolateral processes short, 0.35 Plt length, straight, oriented posterolaterally. Antenna I (Fig. 7 E) length 0.16 body length; flagellum with 5 articles. Antenna II (Fig. 7 A) length 0.69 body length; article 3 dorsal projection triangular, projection length 0.38 article 3 length; article 5 projection length 0.43 article 5 length; flagellum with 19 articles. Mandible (Fig. 8 B, C) incisor with 5 cusps, left Md lacinia mobilis with 4 cusps. Maxillipeds (Fig. 8 A) left Mxp with 4 coupling hooks; right Mxp with 3 coupling hooks. Pereopod II (Fig. 7 C) length 0.34 body length. PIII length 0.35 body length. PIV length 0.37 body length. PV length 0.64 body length. PVI (Fig. 7 D) length 0.68 body length. PVII length 0.62 body length; PV – VII lengths distinctly exceeding PI – IV lengths, PVII shorter than PVI. Pleopod I (Figs 9 A, 26 J) medial lobes subtriangular, projecting caudolaterally; adjoining at the apex. Pleopod II (Fig. 9 B, C) protopod semi-circular, with distal lobe extending beyond protopod distal margin; endopod stylet 1.8 protopod length. Female. Differs from male in the following characters: Body (Fig. 6 A) length 2.4 width; anterior body length (Ceph – Prn 4) 0.95 posterior body length (Prn 5 – Plt). Cephalothorax (Fig. 6 A, C) length 0.26 width, 0.07 body length, width 0.60 body width; frontal margin width 0.51 Ceph width. Pereonite 4 (Fig. 6 A) lateral margin length 1.24 Prn 5 lateral margin length. Pleotelson (Figs 6 A, 26 I) length 0.81 width, 0.25 body length; posterolateral processes 0.32 Plt length. Antenna I (Fig. 6 A) length 0.14 body length; flagellum with 4 articles. Antenna II (Fig. 6 A) length 0.63 body length; flagellum with 16 articles. Operculum (Fig. 26 I) length 0.97 width, 0.81 Plt length; distal margin with numerous, evenly distributed long setae; lateral margins with fewer, evenly distributed short setae.