Haploniscus apaticus Knauber & Riehl, 2025

Haploniscus apaticus Knauber & Riehl sp. nov.

Figs 6 View Figure 6 , 7 View Figure 7 , 8 View Figure 8 , 9 View Figure 9 , 26 View Figure 26

Holotype.

SKB Hap 08, adult male (stage VI), 3.3 mm, MIMB 50307 View Materials . GoogleMaps

Paratypes.

SKB Hap 18, adult female (stage IV), 3.2 mm, MIMB 50308 GoogleMaps ; SKB Hap 48, adult female (stage IV; genome), SMF 56565 GoogleMaps .

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   GoogleMaps .

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 View Figure 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 View Figure 6 ) 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 View Figure 6 ) 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 View Figure 6 ) 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 View Figure 6 , 26 J View Figure 26 ) 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 View Figure 7 ) length 0.16 body length; flagellum with 5 articles.

Antenna II (Fig. 7 A View Figure 7 ) 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 View Figure 8 ) incisor with 5 cusps, left Md lacinia mobilis with 4 cusps.

Maxillipeds (Fig. 8 A View Figure 8 ) left Mxp with 4 coupling hooks; right Mxp with 3 coupling hooks.

Pereopod II (Fig. 7 C View Figure 7 ) 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 View Figure 7 ) 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 View Figure 9 , 26 J View Figure 26 ) medial lobes subtriangular, projecting caudolaterally; adjoining at the apex.

Pleopod II (Fig. 9 B, C View Figure 9 ) 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 View Figure 6 ) length 2.4 width; anterior body length (Ceph – Prn 4) 0.95 posterior body length (Prn 5 – Plt).

Cephalothorax (Fig. 6 A, C View Figure 6 ) 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 View Figure 6 ) lateral margin length 1.24 Prn 5 lateral margin length.

Pleotelson (Figs 6 A View Figure 6 , 26 I View Figure 26 ) length 0.81 width, 0.25 body length; posterolateral processes 0.32 Plt length.

Antenna I (Fig. 6 A View Figure 6 ) length 0.14 body length; flagellum with 4 articles.

Antenna II (Fig. 6 A View Figure 6 ) length 0.63 body length; flagellum with 16 articles.

Operculum (Fig. 26 I View Figure 26 ) length 0.97 width, 0.81 Plt length; distal margin with numerous, evenly distributed long setae; lateral margins with fewer, evenly distributed short setae.