Niphargus entlebuchensis Knüsel, Alther, Zakšek, Fišer & Altermatt, 2026, sp. nov.

Niphargus entlebuchensis sp. nov. Type locality. Schrattenfluh karstic mountain ridge in central Switzerland. Holotype collected from a cave (Silwängenhöhle, WGS 84 46.83435, 7.98135, 1567 m a. s. l., approx. 100–150 m within the cave, - 25 m depth, in small and permanently flowing seepage water, Martin Trüssel leg.). Paratypes collected from drinking water provisioning wells (Imbrig Quellen, Wasserversorgungs-Genossenschaft Marbach, WGS 84 46.82628, 7.94073, 1433 m a. s. l., Bruno Renggli leg.). Material examined. Holotype: • Male (id 28279), 18.5 mm long. Dissected, body appendages mounted on slides. Stored in the collection of Naturéum, Muséum cantonal des sciences naturelles, Département de Zoologie, Lausanne, Switzerland, under voucher numbers GBIFCH 01224687, GBIFCH 01224688, and GBIFCH 10031611. Paratypes: • One male (id 22873) and two females (id 22871, id 22874) of respective lengths 13.4, 12.6, and 13.2 mm. Dissected, body appendages mounted on slides. Stored in the collection of Naturéum, Muséum cantonal des sciences naturelles, Département de Zoologie, Lausanne, Switzerland, under voucher numbers GBIFCH 01224689 – GBIFCH 01224692 and GBIFCH 10031612 – GBIFCH 10031614. Etymology. The name “ entlebuchensis ” is derived from the region Entlebuch (and the UNESCO Biosphäre Entlebuch), where the species was discovered. The region itself is named after the stream Entle, whose name is probably of Celtic origin and is thought to mean “ to spring forth ” or “ to emerge ”, as water from a spring (Greule 2014). Morphological diagnosis. Slender and mid to large sized Niphargus. Maxilla I outer lobe with 9–11 bifurcate spines, the inner-most spine may have an additional denticle. Propodi of gnathopods mid-to large, palm oblique. Pereopod dactyli III – VII with a single spine accompanied with a tiny seta at the base of the nail. Uropod I rami sexually moderately dimorphic; uropod III sexually dimorphic and elongated in males. At the base of uropod I 2, rarely 1 spine (s). Molecular diagnosis. COI: ‘ C’ at position 456 and ‘ G’ at position 586, rDNC support 100 %. The alignment is available in Suppl. material 4. Description. Body length. Up to 18.5 mm. Head, pereonites, pleonites and urosomites (Fig. 4). Head approximately 10 % of body length; rostrum absent. Pereonites I – VI without setae; pereonite VII with 1 postero-ventral seta. Pleonites I – III with up to 3 slender posterodorsal setae. Urosomite I 1 postero-dorso-lateral thin spine; urosomite II 2–3 postero-dorso-lateral 3 spines; and posterior margin of urosomite III without spines. At the base of uropod I 2, rarely 1 spine (s). Epimeral plates. Epimeral plate I with pointed postero-ventral corner and angular convex posterior margin with 4 spines / setae. Epimeral plate II with approximately perpendicular, pointed postero-ventral corner and slightly to distinctly convex posterior and ventral margins; ventral and posterior margin with 2–3 spines and 3–5 setae, respectively. Epimeral plate III with slightly yet distinctly inclined, pointed postero-ventral corner; concave to sinusoid posterior margin and slightly convex ventral margins; ventral and posterior margin with 3 setae and 4–6 setae, respectively. Antennae (Fig. 5). Antenna I (Fig. 5 A) 49–51 % of body length. Flagellum of antenna I with up to 22–24 articles; each article with 1 aesthetasc. Peduncle articles lengths progressively shorter. Proximal article of peduncle dorso-distally slightly produced. Accessory flagellum biarticulated; distal article shorter than half of proximal article length. Antenna I: antenna II length 1: 0.44–0.48. Flagellum of antenna II (Fig. 5 B) with 10–11 articles; aesthetascs absent. Peduncle article 4 slightly shorter than peduncle article 5; flagellum slightly shorter than length of peduncle articles (4 + 5). Mouth parts (Fig. 6). Labrum (Fig. 6 A) of roughly triangular shape, typical of the genus. Labium (Fig. 6 B) bilobate, inner lobes slightly exceeding half of the length of the outer lobes. Left mandible (Fig. 6 C, D). Incisor with 5 teeth, lacinia mobilis with 4 teeth; a long row of serrated setae between lacinia mobilis and molar process. A long seta at the base of the molar process. Right mandible (Fig. 6 E, F). Incisor process with 4 teeth, lacinia mobilis bifurcate with 9–13 small denticles, a row of denticulate setae and molar process with a long basal seta. Second mandibular palp (Fig. 6 C, E) article: distal article length 1: 1.15–1.18. Proximal palp article without setae; second article with 15–18 setae; distal article with 1–2 groups of A setae with totally 6–10 setae; 3–4 B groups with totally 9–12 setae; 18–30 D setae; 6–8 E setae. Maxilla I (Fig. 6 G) palp biarticulated; distal article with 5–7 apical setae. Outer lobe of maxilla I with 9–11 spines; inner spine with 2–3 denticles, the rest bifurcate; inner lobe with 2–3 setae. Maxilla II (Fig. 6 H) bilobed; inner lobe slightly smaller than outer lobe; both of them setose apically. Maxilliped (Fig. 6 I) palp article 2 with 8–11 rows of setae along inner margin; distal article with a pair of dorsal setae and 2 small setae at the base of the nail; outer lobe with 12–14 flattened spines and 4–7 serrated setae; inner lobe with 4 flattened apical spines, 1 subapical spine and 6–8 denticulated setae. Gnathopods (Fig. 7). Gnathopod I (Fig. 7 A) coxal plate of rhomboid shape with rounded corners; anterior and ventral margins of coxa I with 9–10 setae. Basis armed with long setae at anterior and posterior margins. Ischium with posterodistal row of 9–14 setae. Carpus: propodus length 1: 0.73–0.94. Anterior margin of carpus with one distal group of setae; carpus posteriorly with transverse rows of setae proximally, a row of lateral setae, a short row of setae at the base medially and submarginal setae groups (not all setae illustrated in detail); posterior enlargement wide, inserted medially. Propodus length: width 1: 1.17–1.30; diagonal: length 1: 0.76–0.88; diagonal: width 1: 0.87–0.93. Along posterior margin 6–9 rows of 3 to 6 denticulate setae. Anterior margin and sub-margin with 2–4 setae groups, totally with 7–20 setae; antero-distal group of setae with 8–13 setae. A group of 4–5 long thin setae proximally to palmar spine; small groups of surface setae present (not illustrated). Palmar corner with strong palmar spine, single short supporting spine on inner side and 3–4 denticulate spines on outer side. Total dactylus length: nail length 1: 0.2–0.25; along anterior margin 7–10 setae (single or in groups); short setae along inner margin present. Gnathopod II (Fig. 7 B) coxal plate width: depth 1: 0.9–1; anterior and ventral margin with 8–13 setae. Carpus: propodus length 1: 1.14–1.37. Anterior margin of carpus only with one distal group of setae; posterior margin densely setose, not deviating from the commonly observed setal patterns, a row of lateral setae, a short row of setae at the base medially and submarginal setae groups (not all setae illustrated in detail); posterior enlargement wide, inserted medially. Gnathopod II propodus size (length + width + diagonal) 0.25–0.27 body length; the length of gnathopod I propodus: the length of gnathopod II propodus 1: 1.17–1.45. Propodus length: width 1: 1.00–1.06; diagonal: length 1: 0.87–0.99; diagonal: width 1: 0.87–0.99. Posterior margin with 8–10 rows of denticulate setae. Anterior margin and sub-margin with 1–4 setae groups, totally with 2–14 setae; anterodistal group of setae with 7–13 setae. A group of 4–5 long thin setae proximally to palmar spine; small groups of surface setae present (not illustrated). Palmar corner with strong palmar spine, single short supporting spine on inner side and 1–3 denticulate spines on outer side. Total dactylus length: nail length 1: 0.20–0.25. Along anterior margin 12–14 setae (single and in groups); short setae along inner margin present. Pereopods (Fig. 8). Pereopods III – IV (Fig. 8 A, B) of subequal lengths, in ratio 1.0: 0.95–1.00. Coxal plate III width: depth 1: 0.9–1.0; along antero-ventral margin 9–12 setae. Dactylus III with dorsal plumose seta; at the base of nail a spine and a seta. Coxal plate IV width: depth 1: 0.8–0.9; posteriorly slightly concave; along antero-ventral margin 9–13 setae. Propodus: dactylus lengths 1: 0.45–0.48; total dactylus length: nail length 1: 0.45–0.55. Dactylus IV with dorsal plumose seta; at the base of nail a spine and a seta. Pereopods V – VII (Fig. 8 C – E). Pereopod V length: VI length: VII length 1: 1.30–1.40: 1.30–1.37. Pereopod VII length 50–60 % body length. Coxal plate V. Anterior lobe with 5 setae and posterior lobe with 1 seta posteriorly. Basis of pereopod V length: width 1: 0.51–0.55; posterior margin slightly convex, with weak postero-distal lobe; 11–14 setae posteriorly and anteriorly 7 groups of multiple or single spines and / or setae, thereof 6 at the anterior margin and 1 group at the antero-distal corner. Dactylus of pereopod V with dorsal plumose seta; at the base of nail a spine and a seta. Coxal plate VI. Posterior lobe with 1 posterior seta. Basis of pereopod VI length: width 1: 0.50–0.55; posterior margin slightly convex, with weak postero-distal lobe; 14 setae posteriorly and anteriorly 8 groups of multiple or single slender spines and / or setae, thereof 7 at the anterior margin and 1 group at the antero-distal corner. Dactylus of pereopod VI with dorsal plumose seta; at the base of nail a spine and a seta. Coxal plate VII semiovoid with 1 seta posteriorly. Basis of pereopod VII length: width 1: 0.50–0.53; posterior margin slightly convex, with weak postero-distal lobe; 12–15 setae posteriorly and anteriorly 7 groups of multiple or single spines and / or setae, thereof 6 at the anterior margin and 1 group at the antero-distal corner. Propodus length: dactylus length 1: 0.20–0.25. Dactylus of pereopod VII with dorsal plumose seta; at the base of nail a spine and a seta. Gills II – VI large, irregularly ovoid (data not shown in figure). Pleopods (Fig. 9 A). Pleop