taxonID	type	description	language	source
CF49EC2A480257119CF9275091312ABE.taxon	description	Figs 6, 7, 8, 9, 26	en	Knauber, Henry, Schell, Tilman, Brandt, Angelika, Riehl, Torben (2025): Across trench and ridge: description of five new species of the Haploniscus belyaevi Birstein, 1963 species complex (Isopoda, Haploniscidae) from the Kuril-Kamchatka Trench region. Zoosystematics and Evolution 101 (2): 813-853, DOI: 10.3897/zse.101.137663
CF49EC2A480257119CF9275091312ABE.taxon	distribution	Distribution. Northwest Pacific, Sea of Okhotsk, Kuril Basin, depth 3351 – 3366 m. Visualized in Fig. 27.	en	Knauber, Henry, Schell, Tilman, Brandt, Angelika, Riehl, Torben (2025): Across trench and ridge: description of five new species of the Haploniscus belyaevi Birstein, 1963 species complex (Isopoda, Haploniscidae) from the Kuril-Kamchatka Trench region. Zoosystematics and Evolution 101 (2): 813-853, DOI: 10.3897/zse.101.137663
CF49EC2A480257119CF9275091312ABE.taxon	etymology	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. ”	en	Knauber, Henry, Schell, Tilman, Brandt, Angelika, Riehl, Torben (2025): Across trench and ridge: description of five new species of the Haploniscus belyaevi Birstein, 1963 species complex (Isopoda, Haploniscidae) from the Kuril-Kamchatka Trench region. Zoosystematics and Evolution 101 (2): 813-853, DOI: 10.3897/zse.101.137663
CF49EC2A480257119CF9275091312ABE.taxon	diagnosis	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.	en	Knauber, Henry, Schell, Tilman, Brandt, Angelika, Riehl, Torben (2025): Across trench and ridge: description of five new species of the Haploniscus belyaevi Birstein, 1963 species complex (Isopoda, Haploniscidae) from the Kuril-Kamchatka Trench region. Zoosystematics and Evolution 101 (2): 813-853, DOI: 10.3897/zse.101.137663
CF49EC2A480257119CF9275091312ABE.taxon	description	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.	en	Knauber, Henry, Schell, Tilman, Brandt, Angelika, Riehl, Torben (2025): Across trench and ridge: description of five new species of the Haploniscus belyaevi Birstein, 1963 species complex (Isopoda, Haploniscidae) from the Kuril-Kamchatka Trench region. Zoosystematics and Evolution 101 (2): 813-853, DOI: 10.3897/zse.101.137663
BC04A7E2765F554B8A48FEB397DB12D1.taxon	description	Figs 1, 2, 3, 4, 5, 26	en	Knauber, Henry, Schell, Tilman, Brandt, Angelika, Riehl, Torben (2025): Across trench and ridge: description of five new species of the Haploniscus belyaevi Birstein, 1963 species complex (Isopoda, Haploniscidae) from the Kuril-Kamchatka Trench region. Zoosystematics and Evolution 101 (2): 813-853, DOI: 10.3897/zse.101.137663
BC04A7E2765F554B8A48FEB397DB12D1.taxon	distribution	Distribution. Northwest Pacific, Sea of Okhotsk, Kuril Basin, and abyssal regions to the northwest of the Kuril-Kamchatka Trench, depth 3299 – 3386 m. Given its occurrence on both sides of the Kuril Island Ridge, it might be possible that this species’ lowest bathymetric limit might lie even shallower, as it most likely dispersed across the Bussol Strait in one or other direction with a maximum depth of 2,350 m. The original species description of H. belyaevi depicts a distributional range extending far into the KKT area, yet despite sampling these areas during the above-mentioned expeditions, H. belyaevi was solely recorded in the vicinity of the Bussol Strait. One can therefore only hypothesize that Birstein, potentially due to limited material, lumped the distributional patterns of multiple belyaevi - complex members together, not realizing that he was dealing with multiple species. Visualized in Fig. 27.	en	Knauber, Henry, Schell, Tilman, Brandt, Angelika, Riehl, Torben (2025): Across trench and ridge: description of five new species of the Haploniscus belyaevi Birstein, 1963 species complex (Isopoda, Haploniscidae) from the Kuril-Kamchatka Trench region. Zoosystematics and Evolution 101 (2): 813-853, DOI: 10.3897/zse.101.137663
BC04A7E2765F554B8A48FEB397DB12D1.taxon	diagnosis	Diagnosis. The species differs from other members of the belyaevi - complex in the following characters: rostrum curved upwards, anteriorly flat; Prn 1 anterior tergite margin delicately serrated, setose; Prn 1 anterolateral angles with minute acute projection; posterolateral processes short, more than 0.10 Plt length, curved in males, oriented posteriorly.	en	Knauber, Henry, Schell, Tilman, Brandt, Angelika, Riehl, Torben (2025): Across trench and ridge: description of five new species of the Haploniscus belyaevi Birstein, 1963 species complex (Isopoda, Haploniscidae) from the Kuril-Kamchatka Trench region. Zoosystematics and Evolution 101 (2): 813-853, DOI: 10.3897/zse.101.137663
BC04A7E2765F554B8A48FEB397DB12D1.taxon	description	Description. Male. Body (Figs 1 B, 2 B) length 2.3 width; subrectangular; 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 (Figs 1 B, 2 B, D) length 0.38 width, 0.10 body length, width 0.58 body width; frontal margin width 0.50 Ceph width; rostrum curved upwards, frontally plane. Pereonite 1 (Figs 1 B, 2 B) anterior tergite margin through Prn 5 anterior tergite margin delicately serrated, setose; Prn 1 – 5 anterolateral angles slightly projecting; Prn 1 – 4 posterolateral angles slightly projecting; Prn 4 lateral margin length 1.04 Prn 5 lateral margin length. Pleotelson (Figs 1 B, 2 B, 26 H) length 0.74 width, 0.25 body length, rectangular, posterior margin rounded, convex; tergite surface smooth; with posterolateral tergal ridge between uropod insertion and posterolateral process; posterolateral processes short, 0.31 Plt length, curved, oriented posteriorly. Antenna I (Fig. 3 B) length 0.17 body length; flagellum with 5 articles. Antenna II (Fig. 3 A) length 0.31 body length (without missing peduncular article 6 and flagellum); article 3 dorsal projection triangular, projection length 0.30 article 3 length; article 5 projection length 0.28 article 5 length; flagellum with 17 articles (inferred from male paratype). Mandible (Fig. 4 B, C) incisor with 5 cusps, left Md lacinia mobilis with 4 cusps. Maxillipeds (Fig. 4 A) with 3 coupling hooks each. Pereopod I (Fig. 3 C) length 0.40 body length. PII (Fig. 3 D) length 0.49 body length. PIII length 0.53 body length. PIV length 0.53 body length. PV length 0.64 body length. PVI (Fig. 3 E) length 0.71 body length; P lengths gradually increasing from PI to PVI, PVII shorter than PVI. Pleopod I (Figs 5 A, 26 H) medial lobes subtriangular, projecting caudolaterally; separated at the apex by a narrow gap. Pleopod II (Fig. 5 B, C) protopod semi-circular, with distal lobe extending beyond protopod distal margin; endopod stylet 1.6 protopod length. Female. Differs from male in the following characters: Body (Fig. 2 A) length 2.3 width; oval; anterior body length (Ceph – Prn 4) 0.95 posterior body length (Prn 5 – Plt). Cephalothorax (Fig. 2 A, C) length 0.48 width, 0.13 body length, width 0.60 body width; frontal margin width 0.47 Ceph width. Pereonite (Fig. 2 A) 4 lateral margin length 1.05 Prn 5 lateral margin length. Pleotelson (Figs 2 A, 26 G) length 0.83 width, 0.27 body length, trapezoidal; posterolateral processes 0.20 Plt length, straight. Antenna I (Fig. 2 A) length 0.16 body length; flagellum with 4 articles. Antenna II (Fig. 2 A) length 0.57 body length; flagellum with 12 articles. Operculum (Fig. 26 G) Length 1.0 width, 0.77 Plt length; distal margin with numerous, evenly distributed long setae.	en	Knauber, Henry, Schell, Tilman, Brandt, Angelika, Riehl, Torben (2025): Across trench and ridge: description of five new species of the Haploniscus belyaevi Birstein, 1963 species complex (Isopoda, Haploniscidae) from the Kuril-Kamchatka Trench region. Zoosystematics and Evolution 101 (2): 813-853, DOI: 10.3897/zse.101.137663
13D95A2E853659AC950D7E6D636BAF09.taxon	description	Figs 1, 10, 11, 12, 13, 26	en	Knauber, Henry, Schell, Tilman, Brandt, Angelika, Riehl, Torben (2025): Across trench and ridge: description of five new species of the Haploniscus belyaevi Birstein, 1963 species complex (Isopoda, Haploniscidae) from the Kuril-Kamchatka Trench region. Zoosystematics and Evolution 101 (2): 813-853, DOI: 10.3897/zse.101.137663
13D95A2E853659AC950D7E6D636BAF09.taxon	distribution	Distribution. Northwest Pacific, Sea of Okhotsk, Kuril Basin, depth 3210 – 3366 m. Visualized in Fig. 27.	en	Knauber, Henry, Schell, Tilman, Brandt, Angelika, Riehl, Torben (2025): Across trench and ridge: description of five new species of the Haploniscus belyaevi Birstein, 1963 species complex (Isopoda, Haploniscidae) from the Kuril-Kamchatka Trench region. Zoosystematics and Evolution 101 (2): 813-853, DOI: 10.3897/zse.101.137663
13D95A2E853659AC950D7E6D636BAF09.taxon	etymology	Etymology. From “ Erebus ” (Ancient Greek: Ἔρεβος), the Greek mythological personification of darkness. It is a noun in apposition.	en	Knauber, Henry, Schell, Tilman, Brandt, Angelika, Riehl, Torben (2025): Across trench and ridge: description of five new species of the Haploniscus belyaevi Birstein, 1963 species complex (Isopoda, Haploniscidae) from the Kuril-Kamchatka Trench region. Zoosystematics and Evolution 101 (2): 813-853, DOI: 10.3897/zse.101.137663
13D95A2E853659AC950D7E6D636BAF09.taxon	diagnosis	Diagnosis. Haploniscus erebus sp. nov. differs from other species of the belyaevi - complex in the following characters: rostrum straight, near triangular in lateral view; Plt shape rectangular, posterior margin straight in males; posterolateral processes long, more than 0.50 Plt length in males, straight, oriented posteriorly.	en	Knauber, Henry, Schell, Tilman, Brandt, Angelika, Riehl, Torben (2025): Across trench and ridge: description of five new species of the Haploniscus belyaevi Birstein, 1963 species complex (Isopoda, Haploniscidae) from the Kuril-Kamchatka Trench region. Zoosystematics and Evolution 101 (2): 813-853, DOI: 10.3897/zse.101.137663
13D95A2E853659AC950D7E6D636BAF09.taxon	description	Description. Male. Body (Figs 1 C, 10 B) length 2.2 width; subrectangular; anterior body length (Ceph – Prn 4) 1.1 posterior body length (Prn 5 – Plt); lateral margin interrupted between Prn 7 and Plt, otherwise continuous. Cephalothorax (Figs 1 C, 10 B, D) length 0.45 width, 0.13 body length, width 0.61 body width; frontal margin width 0.50 Ceph width; rostrum straight, near triangular laterally. Pereonite 1 (Figs 1 C, 10 B) posterior tergite margin through Prn 5 anterior tergite margin delicately serrated, setose; Prn 2 – 5 anterolateral angles slightly projecting; Prn 2 – 4 posterolateral angles slightly projecting; Prn 4 lateral margin length 0.89 Prn 5 lateral margin length. Pleotelson (Figs 1 C, 10 B, 26 B) length 0.64 width, 0.23 body length, rectangular, posterior margin straight; tergite surface smooth; with posterolateral tergal ridge between uropod insertion and posterolateral process; posterolateral processes long, 0.53 Plt length, straight, oriented posteriorly. Antenna I (Fig. 11 B) length 0.18 body length; flagellum with 6 articles. Antenna II (Fig. 11 A) length 0.68 body length; article 3 dorsal projection triangular, projection length 0.42 article 3 length; article 5 projection length 0.28 article 5 length; flagellum with 16 articles. Mandible (Fig. 12 B, C) incisor with 5 cusps, left Md lacinia mobilis with 5 cusps. Maxillipeds (Fig. 12 A) with 3 coupling hooks each. Pereopod I (Fig. 11 C) length 0.43 body length. PII (Fig. 11 D) length 0.49 body length. PIII length 0.58 body length. PIV length 0.60 body length. PV length 0.75 body length. PVI (Fig. 11 E) length 0.81 body length. PVII length 0.79 body length; P lengths gradually increasing from PI to PVI, PVII shorter than PVI. Pleopod I (Figs 13 A, 26 B) medial lobes subtriangular, projecting caudolaterally; separated at the apex by a narrow gap. Pleopod II (Fig. 13 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. 10 A) length 2.3 width; oval; anterior body length (Ceph – Prn 4) 0.99 posterior body length (Prn 5 – Plt). Cephalothorax (Fig. 10 A, C) length 0.36 width, 0.09 body length, width 0.59 body width; frontal margin width 0.55 Ceph width. Pereonite 4 (Fig. 10 A) lateral margin length 1.0 Prn 5 lateral margin length. Pleotelson (Figs 10 A, 26 A) length 0.74 width, 0.24 body length, trapezoidal, posterior margin rounded, convex; posterolateral processes short, 0.34 Plt length, oriented posterolaterally. Antenna I (Fig. 10 A) length 0.14 body length; flagellum with 4 articles. Antenna II (Fig. 10 A) length 0.61 body length; flagellum with 13 articles. Operculum (Fig. 26 A) length 0.93 width, 0.81 Plt length; distal margin with numerous, evenly distributed long setae; lateral margins with fewer, evenly distributed short setae.	en	Knauber, Henry, Schell, Tilman, Brandt, Angelika, Riehl, Torben (2025): Across trench and ridge: description of five new species of the Haploniscus belyaevi Birstein, 1963 species complex (Isopoda, Haploniscidae) from the Kuril-Kamchatka Trench region. Zoosystematics and Evolution 101 (2): 813-853, DOI: 10.3897/zse.101.137663
C0C4A9BB10B053E2B91F5B5522A6CC44.taxon	description	Figs 1, 14, 15, 16, 17, 26	en	Knauber, Henry, Schell, Tilman, Brandt, Angelika, Riehl, Torben (2025): Across trench and ridge: description of five new species of the Haploniscus belyaevi Birstein, 1963 species complex (Isopoda, Haploniscidae) from the Kuril-Kamchatka Trench region. Zoosystematics and Evolution 101 (2): 813-853, DOI: 10.3897/zse.101.137663
C0C4A9BB10B053E2B91F5B5522A6CC44.taxon	distribution	Distribution. Northwest Pacific, Kuril-Kamchatka Trench, depth 5493 – 8191 m. Visualized in Fig. 27.	en	Knauber, Henry, Schell, Tilman, Brandt, Angelika, Riehl, Torben (2025): Across trench and ridge: description of five new species of the Haploniscus belyaevi Birstein, 1963 species complex (Isopoda, Haploniscidae) from the Kuril-Kamchatka Trench region. Zoosystematics and Evolution 101 (2): 813-853, DOI: 10.3897/zse.101.137663
C0C4A9BB10B053E2B91F5B5522A6CC44.taxon	etymology	Etymology. The specific epithet “ hades ” is a noun in apposition derived from “ Hades ” (Ancient Greek: Ἅιδης), the god and ruler of the underworld in Greek mythology. This name refers to this species distributional range within the hadal depths of the Kuril-Kamchatka Trench and the novel feature of the pleotelson posterior margin tergal plates projecting above the uropods in males. These render the uropods “ invisible ” from dorsal view, reminiscent of Hades’ cap of invisibility.	en	Knauber, Henry, Schell, Tilman, Brandt, Angelika, Riehl, Torben (2025): Across trench and ridge: description of five new species of the Haploniscus belyaevi Birstein, 1963 species complex (Isopoda, Haploniscidae) from the Kuril-Kamchatka Trench region. Zoosystematics and Evolution 101 (2): 813-853, DOI: 10.3897/zse.101.137663
C0C4A9BB10B053E2B91F5B5522A6CC44.taxon	diagnosis	Diagnosis. Haploniscus hades sp. nov. differs from other species of the belyaevi - complex in the following characters: rostrum curved upwards, basally with dorsal bulge in males; Plt with posterolateral tergal ridge on posterolateral process and posterior margin tergal plates projecting above uropods (solely present in sister species H. kerberos sp. nov. otherwise); AII article 3 dorsal projection hook-shaped; Plp I distally with hook-shaped projection.	en	Knauber, Henry, Schell, Tilman, Brandt, Angelika, Riehl, Torben (2025): Across trench and ridge: description of five new species of the Haploniscus belyaevi Birstein, 1963 species complex (Isopoda, Haploniscidae) from the Kuril-Kamchatka Trench region. Zoosystematics and Evolution 101 (2): 813-853, DOI: 10.3897/zse.101.137663
C0C4A9BB10B053E2B91F5B5522A6CC44.taxon	description	Description. Male. Body (Figs 1 A, 14 B) length 2.3 width; oval; anterior body length (Ceph – Prn 4) 0.84 posterior body length (Prn 5 – Plt); lateral margin continuous. Cephalothorax (Figs 1 A, 14 B, D) length 0.28 width, 0.07 body length, width 0.56 body width; frontal margin width 0.53 Ceph width; rostrum curved upwards, basally with dorsal bulge. Pereonite 1 (Figs 1 A, 14 B) posterior tergite margin through Prn 5 anterior tergite margin delicately serrated, setose; Prn 2 – 4 anterolateral angles slightly projecting; Prn 2 – 4 posterolateral angles slightly projecting; Prn 4 lateral margin length 0.89 Prn 5 lateral margin length; Prn 5 anterolateral angle not projecting, rectangular. Pleotelson (Figs 1 A, 14 B, 26 F) length 0.75 width, 0.27 body length, trapezoidal, posterior margin concave; tergite surface tuberculate, less distinct than in remaining body; with posterolateral tergal ridge on posterolateral process and posterior margin tergal plates projecting above uropods; posterolateral processes minute, 0.04 Plt length, straight, oriented posteriorly. Antenna I (Fig. 15 B) length 0.17 body length; flagellum with 6 articles. Antenna II (Fig. 15 A) length 0.67 body length; article 3 dorsal projection hook-shaped, projection length 0.39 article 3 length; article 5 projection length 0.26 article 5 length; flagellum with 16 articles. Mandible (Fig. 16 B, C) incisor with 6 cusps, left Md lacinia mobilis with 5 cusps. Maxillipeds (Fig. 16 A) with 3 coupling hooks each. Pereopod I (Fig. 15 C) length 0.41 body length. PIII length 0.53 body length. PIV length 0.54 body length. PV length 0.67 body length. PVI (Fig. 15 E) length 0.70 body length. PVII length 0.69 body length; P lengths gradually increasing from PI to PVI, PVII shorter than PVI. Pleopod I (Figs 17 A, 26 F) medial lobes convexly rounded, tapering to an obtuse point; distally with hook-shaped projection; separated at the apex by a narrow gap. Pleopod II (Fig. 17 B, C) protopod elongated, suboval; endopod stylet 2.0 protopod length. Female. Differs from male in the following characters: Body (Fig. 14 A) length 2.4 width; anterior body length (Ceph – Prn 4) 1.0 posterior body length (Prn 5 – Plt). Cephalothorax (Fig. 14 A, C) length 0.52 width, 0.14 body length, width 0.63 body width; frontal margin width 0.55 Ceph width. Pereonite 4 (Fig. 14 A) lateral margin length 0.93 Prn 5 lateral margin length. Pleotelson (Figs 14 A, 26 E) length 0.75 width, 0.25 body length, posterior margin straight; posterolateral processes 0.08 Plt length. Antenna I (Fig. 14 A) length 0.15 body length; flagellum with 4 articles. Antenna II (Fig. 14 A) length 0.70 body length; flagellum with 11 articles. Operculum (Fig. 26 E) length 1.1 width, 0.74 Plt length; distal margin with numerous, evenly distributed long setae; lateral margins with up to 3 short setae each.	en	Knauber, Henry, Schell, Tilman, Brandt, Angelika, Riehl, Torben (2025): Across trench and ridge: description of five new species of the Haploniscus belyaevi Birstein, 1963 species complex (Isopoda, Haploniscidae) from the Kuril-Kamchatka Trench region. Zoosystematics and Evolution 101 (2): 813-853, DOI: 10.3897/zse.101.137663
A19368E9BC2F5FA4BDDF0F0F45D53813.taxon	description	Figs 18, 19, 20, 21, 26	en	Knauber, Henry, Schell, Tilman, Brandt, Angelika, Riehl, Torben (2025): Across trench and ridge: description of five new species of the Haploniscus belyaevi Birstein, 1963 species complex (Isopoda, Haploniscidae) from the Kuril-Kamchatka Trench region. Zoosystematics and Evolution 101 (2): 813-853, DOI: 10.3897/zse.101.137663
A19368E9BC2F5FA4BDDF0F0F45D53813.taxon	distribution	Distribution. Northwest Pacific, abyssal regions adjacent to the Kuril-Kamchatka Trench, depth 4469 – 5755 m. Visualized in Fig. 27.	en	Knauber, Henry, Schell, Tilman, Brandt, Angelika, Riehl, Torben (2025): Across trench and ridge: description of five new species of the Haploniscus belyaevi Birstein, 1963 species complex (Isopoda, Haploniscidae) from the Kuril-Kamchatka Trench region. Zoosystematics and Evolution 101 (2): 813-853, DOI: 10.3897/zse.101.137663
A19368E9BC2F5FA4BDDF0F0F45D53813.taxon	etymology	Etymology. As a noun in apposition, the epithet “ kerberos ” refers to “ Kerberos ” (Ancient Greek Κέρβερος) from Greek mythology, the creature guarding the gates of the underworld. This name relates to this species’ distributional range, which, according to the available data, is limited to the abyssal plains adjacent to the hadal Kuril-Kamchatka Trench.	en	Knauber, Henry, Schell, Tilman, Brandt, Angelika, Riehl, Torben (2025): Across trench and ridge: description of five new species of the Haploniscus belyaevi Birstein, 1963 species complex (Isopoda, Haploniscidae) from the Kuril-Kamchatka Trench region. Zoosystematics and Evolution 101 (2): 813-853, DOI: 10.3897/zse.101.137663
A19368E9BC2F5FA4BDDF0F0F45D53813.taxon	diagnosis	Diagnosis. Haploniscus kerberos sp. nov. is highly similar to H. hades sp. nov. in also possessing the characteristic Plt shape with posterolateral tergal ridges terminating on the posterolateral processes and the posterior margin tergal plates projecting above the uropods. It differs from its sister species in the following characters: rostrum basally without dorsal bulge in males (basally with dorsal bulge in H. hades sp. nov.) and AII article 3 dorsal projection triangular (hook-shaped in H. hades sp. nov.).	en	Knauber, Henry, Schell, Tilman, Brandt, Angelika, Riehl, Torben (2025): Across trench and ridge: description of five new species of the Haploniscus belyaevi Birstein, 1963 species complex (Isopoda, Haploniscidae) from the Kuril-Kamchatka Trench region. Zoosystematics and Evolution 101 (2): 813-853, DOI: 10.3897/zse.101.137663
A19368E9BC2F5FA4BDDF0F0F45D53813.taxon	description	Description. Male. Body (Fig. 18 B) length 2.5 width; oval; anterior body length (Ceph – Prn 4) 1.1 posterior body length (Prn 5 – Plt); lateral margin continuous. Cephalothorax (Fig. 18 B, D) length 0.35 width, 0.08 body length, width 0.59 body width; frontal margin width 0.54 Ceph width; rostrum curved upwards. Pereonite 1 (Fig. 18 B) posterior tergite margin through Prn 5 anterior tergite margin delicately serrated, setose; Prn 2 – 4 anterolateral angles slightly projecting; Prn 2 – 4 posterolateral angles slightly projecting; Prn 4 lateral margin length 0.92 Prn 5 lateral margin length; Prn 5 anterolateral angle not projecting, rectangular. Pleotelson (Figs 18 B, 26 D) length 0.68 width, 0.22 body length, trapezoidal, posterior margin concave; tergite surface tuberculate, less distinct than in remaining body; with posterolateral tergal ridge on posterolateral process and posterior margin tergal plates projecting above uropods; posterolateral processes minute, 0.09 Plt length, straight, oriented posteriorly. Antenna I (Fig. 19 B) length 0.20 body length; flagellum with 6 articles. Antenna II (Fig. 19 A) length 0.77 body length; article 3 dorsal projection triangular, projection length 0.31 article 3 length; article 5 projection length 0.22 article 5 length; flagellum with 16 articles. Mandible (Fig. 20 B, C) incisor with 5 cusps, left Md lacinia mobilis with 4 cusps. Maxillipeds (Fig. 20 A) with 3 coupling hooks each. Pereopod I (Fig. 19 D) length 0.43 body length. PVI (Fig. 19 C) length 0.70 body length; P lengths gradually increasing from PI to PVI, PVII shorter than PVI. Pleopod I missing. Pleopod II (Fig. 21 A, B) protopod elongated, suboval; endopod stylet 2.0 protopod length. Female. Differs from male in the following characters: Body (Fig. 18 A) length 2.7 width; anterior body length (Ceph – Prn 4) 0.94 posterior body length (Prn 5 – Plt). Cephalothorax (Fig. 18 A, C) length 0.50 width, 0.12 body length, width 0.66 body width; frontal margin width 0.55 Ceph width. Pereonite 4 (Fig. 18 A) lateral margin length 0.80 Prn 5 lateral margin length. Pleotelson (Figs 18 A, 26 C) length 0.84 width, 0.24 body length, posterior margin rounded, convex; with posterolateral tergal ridge between uropod insertion and posterolateral process; posterolateral processes short, 0.23 Plt length. Antenna I (Fig. 18 A) length 0.14 body length; flagellum with 4 articles. Antenna II (Fig. 18 A) length 0.67 body length; flagellum with 12 articles. Operculum (Fig. 26 C) length 1.1 width, 0.75 Plt length; distal margin with numerous, evenly distributed long setae; lateral margins with 2 short setae each.	en	Knauber, Henry, Schell, Tilman, Brandt, Angelika, Riehl, Torben (2025): Across trench and ridge: description of five new species of the Haploniscus belyaevi Birstein, 1963 species complex (Isopoda, Haploniscidae) from the Kuril-Kamchatka Trench region. Zoosystematics and Evolution 101 (2): 813-853, DOI: 10.3897/zse.101.137663
F15FB4C76CF051AA9A301C37681E021D.taxon	description	Figs 22, 23, 24, 25, 26	en	Knauber, Henry, Schell, Tilman, Brandt, Angelika, Riehl, Torben (2025): Across trench and ridge: description of five new species of the Haploniscus belyaevi Birstein, 1963 species complex (Isopoda, Haploniscidae) from the Kuril-Kamchatka Trench region. Zoosystematics and Evolution 101 (2): 813-853, DOI: 10.3897/zse.101.137663
F15FB4C76CF051AA9A301C37681E021D.taxon	distribution	Distribution. Only known from type locality. Northwest Pacific, abyssal region adjacent to the Kuril-Kamchatka Trench to the northwest, depth 4769 m. Visualized in Fig. 27.	en	Knauber, Henry, Schell, Tilman, Brandt, Angelika, Riehl, Torben (2025): Across trench and ridge: description of five new species of the Haploniscus belyaevi Birstein, 1963 species complex (Isopoda, Haploniscidae) from the Kuril-Kamchatka Trench region. Zoosystematics and Evolution 101 (2): 813-853, DOI: 10.3897/zse.101.137663
F15FB4C76CF051AA9A301C37681E021D.taxon	etymology	Etymology. The epithet “ nyx, ” a noun in apposition, is derived from “ Nyx ” (Ancient Greek Νύξ), the goddess of the night in Greek mythology.	en	Knauber, Henry, Schell, Tilman, Brandt, Angelika, Riehl, Torben (2025): Across trench and ridge: description of five new species of the Haploniscus belyaevi Birstein, 1963 species complex (Isopoda, Haploniscidae) from the Kuril-Kamchatka Trench region. Zoosystematics and Evolution 101 (2): 813-853, DOI: 10.3897/zse.101.137663
F15FB4C76CF051AA9A301C37681E021D.taxon	diagnosis	Diagnosis. Haploniscus nyx sp. nov. differs from other species of the belyaevi - complex in the following character: pleotelson posterior margin concave in males; Plp I medial lobes convexly rounded, tapering to an obtuse point, distally without a hook-shaped protrusion.	en	Knauber, Henry, Schell, Tilman, Brandt, Angelika, Riehl, Torben (2025): Across trench and ridge: description of five new species of the Haploniscus belyaevi Birstein, 1963 species complex (Isopoda, Haploniscidae) from the Kuril-Kamchatka Trench region. Zoosystematics and Evolution 101 (2): 813-853, DOI: 10.3897/zse.101.137663
F15FB4C76CF051AA9A301C37681E021D.taxon	description	Description. Male. Body (Fig. 22 B) length 2.2 width; subrectangular; anterior body length (Ceph – Prn 4) 0.99 posterior body length (Prn 5 – Plt); lateral margin continuous. Cephalothorax (Fig. 22 B, D) length 0.30 width, 0.07 body length, width 0.55 body width; frontal margin width 0.46 Ceph width; rostrum curved upwards. Pereonite 1 (Fig. 22 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 Prn 5 lateral margin length. Pleotelson (Figs 22 B, 26 L) length 0.72 width, 0.23 body length, trapezoidal, posterior margin concave; tergite surface smooth; with posterolateral tergal ridge between uropod insertion and posterolateral process; posterolateral processes minute, 0.13 Plt length, straight, oriented posteriorly. Antenna I (Fig. 23 B) length 0.16 body length; flagellum with 5 articles. Antenna II (Fig. 23 A) length 0.61 body length; article 3 dorsal projection triangular, projection length 0.36 article 3 length; article 5 projection length 0.23 article 5 length; flagellum with 15 articles. Mandible (Fig. 24 B, C) incisor with 5 cusps, left Md lacinia mobilis with 4 cusps. Maxillipeds (Fig. 24 A) with 3 coupling hooks each. Pereopod I (Fig. 23 C) length 0.37 body length. PII (Fig. 23 D) length 0.45 body length. PIII (Fig. 23 E) length 0.52 body length. PV length 0.65 body length. PVI length 0.70 body length; P lengths gradually increasing from PI to PVI, PVII shorter than PVI. Pleopod I (Figs 25 A, 26 L) medial lobes convexly rounded, tapering to an obtuse point; adjoining at the apex. Pleopod II (Fig. 25 B, C) protopod semi-circular, with distal lobe extending beyond protopod distal margin; endopod stylet 2.1 protopod length. Female. Differs from male in the following characters: Body (Fig. 22 A) length 2.1 width; oval; anterior body length (Ceph – Prn 4) 0.98 posterior body length (Prn 5 – Plt). Cephalothorax (Fig. 22 A, C) length 0.46 width, 0.12 body length, width 0.55 body width; frontal margin width 0.46 Ceph width. Pereonite 4 (Fig. 22 A) lateral margin length 1.05 Prn 5 lateral margin length. Pleotelson (Figs 22 A, 26 K) length 0.83 width, 0.27 body length, posterior margin rounded, convex; posterolateral processes short, 0.19 Plt length. Antenna I (Fig. 22 A) length 0.16 body length; flagellum with 4 articles. Antenna II (Fig. 22 A) length 0.50 body length; flagellum with 15 articles. Operculum (Fig. 26 K) length 0.98 width, 0.66 Plt length; distal margin with numerous, evenly distributed long setae; lateral margins with fewer, evenly distributed short setae.	en	Knauber, Henry, Schell, Tilman, Brandt, Angelika, Riehl, Torben (2025): Across trench and ridge: description of five new species of the Haploniscus belyaevi Birstein, 1963 species complex (Isopoda, Haploniscidae) from the Kuril-Kamchatka Trench region. Zoosystematics and Evolution 101 (2): 813-853, DOI: 10.3897/zse.101.137663
