Haploniscus hades Knauber & Riehl, 2025

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), pp. 813-853 : 813-853

publication ID	https://doi.org/10.3897/zse.101.137663
publication LSID	lsid:zoobank.org:pub:1764B434-B419-4430-B297-6D6380572DFB
DOI	https://doi.org/10.5281/zenodo.15263765
persistent identifier	https://treatment.plazi.org/id/C0C4A9BB-10B0-53E2-B91F-5B5522A6CC44
treatment provided by	Zoosystematics and Evolution by Pensoft
scientific name	Haploniscus hades Knauber & Riehl
status	sp. nov.

Treatment

Haploniscus hades Knauber & Riehl sp. nov.

Figs 1 View Figure 1 , 14 View Figure 14 , 15 View Figure 15 , 16 View Figure 16 , 17 View Figure 17 , 26 View Figure 26

Holotype.

KBII Hap 137, adult male (stage VI), 3.7 mm, SMF 56419 About SMF . GoogleMaps

Paratypes.

KBII Hap 104, adult female (stage IV; genome), SMF 56388 GoogleMaps ; KBII Hap 213, adult female (stage IV), 2.4 mm, SMF 56495 GoogleMaps .

Type locality.

St. SO 250–042, RV “ Sonne ”, KuramBio II expedition, EBS, 7123 m, 45°39.62'N, 152°56.39'E, Northwest Pacific, hadal Kuril-Kamchatka Trench near Bussol Strait GoogleMaps .

Further records.

St. SO 250–020: KBII Hap 116 (adult female) SMF 56399 ; St. SO 250–028: KBII Hap 208 (adult male) SMF 56490 ; St. SO 250–030: KBII Hap 209 (manca) SMF 56491 , KBII Hap 210 (adult female) SMF 56492 ; St. SO 250–040: KBII Hap 220 (ovigerous female) SMF 56502 , KBII Hap 221 (ovigerous female) SMF 56503 , KBII Hap 231 (manca) SMF 56513 , KBII Hap 232 (manca) SMF 56514 ; St. SO 250–042: KBII Hap 105 (manca) SMF 56389 , KBII Hap 106 (manca) SMF 56390 , KBII Hap 165 (adult male) SMF 56447 , KBII Hap 198 (manca) SMF 56480 , KBII Hap 230 (manca) SMF 56512 ; St. SO 250–086: KBII Hap 226 (adult male) SMF 56508 ; St. SO 250–097: KBII Hap 201 (manca) SMF 56483 , KBII Hap 204 (adult male) SMF 56486 , KBII Hap 205 (adult female) SMF 56487 , KBII Hap 206 (ovigerous female) SMF 56488 , KBII Hap 214 (manca) SMF 56496 , KBII Hap 215 (adult female) SMF 56497 , KBII Hap 216 (adult male) SMF 56498 , KBII Hap 217 (adult female) SMF 56499 , KBII Hap 227 (manca) SMF 56509 , KBII Hap 233 (manca) SMF 56515 , KBII Hap 234 (manca) SMF 56516 ; St. SO 250–098: KBII Hap 203 (manca) SMF 56485 .

Distribution.

Northwest Pacific, Kuril-Kamchatka Trench, depth 5493–8191 m. Visualized in Fig. 27 View Figure 27 .

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.

Synonymy.

Haploniscus KKT hadal (see Knauber et al. 2022).

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.

Molecular diagnosis.

Differing in the 16 S gene from other species of the belyaevi - complex in the nucleotide A (position 219 of the alignment) as well as the nucleotides G (103), A (211), T (217), C (232), G (256), T (328), A (349), C (364), C (370), C (442), A (469), C (499), and C (571) of the COI gene.

Description.

Male. Body (Figs 1 A View Figure 1 , 14 B View Figure 14 ) 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 View Figure 1 , 14 B, D View Figure 14 ) 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 View Figure 1 , 14 B View Figure 14 ) 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 View Figure 1 , 14 B View Figure 14 , 26 F View Figure 26 ) 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 View Figure 15 ) length 0.17 body length; flagellum with 6 articles.

Antenna II (Fig. 15 A View Figure 15 ) 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 View Figure 16 ) incisor with 6 cusps, left Md lacinia mobilis with 5 cusps.

Maxillipeds (Fig. 16 A View Figure 16 ) with 3 coupling hooks each.

Pereopod I (Fig. 15 C View Figure 15 ) 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 View Figure 15 ) 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 View Figure 17 , 26 F View Figure 26 ) 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 View Figure 17 ) protopod elongated, suboval; endopod stylet 2.0 protopod length.

Female. Differs from male in the following characters:

Body (Fig. 14 A View Figure 14 ) length 2.4 width; anterior body length (Ceph – Prn 4) 1.0 posterior body length (Prn 5 – Plt).

Cephalothorax (Fig. 14 A, C View Figure 14 ) 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 View Figure 14 ) lateral margin length 0.93 Prn 5 lateral margin length.

Pleotelson (Figs 14 A View Figure 14 , 26 E View Figure 26 ) length 0.75 width, 0.25 body length, posterior margin straight; posterolateral processes 0.08 Plt length.

Antenna I (Fig. 14 A View Figure 14 ) length 0.15 body length; flagellum with 4 articles.

Antenna II (Fig. 14 A View Figure 14 ) length 0.70 body length; flagellum with 11 articles.

Operculum (Fig. 26 E View Figure 26 ) 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.