New species and records of the subterranean amphipod genus Pseudocrangonyx Akatsuka and Komai (Crustacea: Pseudocrangonyctidae), representing the northernmost distribution of the group Author Sídorov, Dmitry Author Labay, Vjacheslav Author Gontcharov, Andrey text Journal of Natural History 2020 2020-12-09 54 27 - 28 1759 1795 http://dx.doi.org/10.1080/00222933.2020.1820092 journal article 10.1080/00222933.2020.1820092 1464-5262 5030637 Pseudocrangonyx borealis sp. nov. ( Figures 2d , 14–17 ) Diagnosis (female) Slender , small-sized amphipod of typical pseudocrangonyctid habitus (sexual dimorphism unknown); eyes absent; body unpigmented (whitish in colour); dorsal surface of body segments smooth, teretial; last mesosomal segment (pereonite VII ) and metasomal segments (pleonites I– III ) bearing 2 fine facial setae each; urosomites I– II with 2 facial setae, ecdysial setae absent; interantennal lobe of head short, rounded, inferior antennal sinus roundish; antenna I about 50% length of body; coxal plates I– IV shallow, sub-rectangular (wider than deep), plates V – VII sub-triangular with moderate anterior lobes; posterodistal corners of pleonal plates I– III broadly roundish; palp mandible article 3 with 2 B-setae, 8 D-setae and 3 E-setae; molar of mandible well developed; propodus of gnathopod I much larger than that of gnathopod II ; carpus of pereopods III – IV with posterior margin unarmed; pereopod V distinctly shorter; pereopods VI and VII equal, about 45% length of body . Uropod I with 1 basofacial spine-seta. Telson with vestigial notch. Body length 4.5 mm ( ♀ ). Material examined Holotype MNHN-IU-2019-3173: ♀ ca. 4.5 mm (oostegites developed, non-setose), RUSSIA , Magadanskaya Oblast , Khasynsky District , basin of the Ola River , Neorchan River , hyporhea, 60.462461 , 151.471181 , elevation 555 m , leg. E. V . Khamenkova, 10 June 2013 . Figure 14. Pseudocrangonyx borealis sp. nov. , holotype MNHN-IU-2019-3173, female, 4.5 mm: (a) antenna I; (b) antenna II; (c) maxilla I; (d) outer plate of maxilla I; (e) lower lip; (f) maxilla II; (g) right mandible; (h) left mandible; (i) upper lip; (j) maxilliped. Scale bars: 0.2 mm. Etymology Species named ‘ borealis ’ (Latin), an adjective that refers to the northern distribution of this species. Gender masculine. Description Female (body 4.5 mm long), MNHN-IU-2019-3173. Head ( Figures 2d , 14a–i ). Antenna I about 33% longer than antenna II; peduncular articles 1–3 in length ratio 1:0.5:0.3; primary flagellum with 13 articles; aesthetascs present. Antenna II peduncular articles 4 and 5 in length ratio 0.9:1; flagellum with 6 articles; calceoli absent. Left mandible incisor 5-dentate; lacinia mobilis 5-dentate; setal row with 3 serrate setae; palp mandible article 3 is 15% longer than article 2; article 3 with 2 B-setae, 8 D-setae and 3 E-setae. Right mandible incisor 5-dentate; lacinia mobilis bifurcate, with numerous small teeth; molar process triturative, with short accessory seta. Lower lip inner lobes absent; mandibular process brief, roundish. Upper lip without peculiarities. Maxilla I inner plate with 3 plumose setae; outer plate with 7 serrate spines; palp article 2 about 2.2× longer than article 1, bearing 3 spines on apex. Maxilla II inner plate with 3 plumose setae in oblique row. Maxilliped inner plate with 2 simple spines and 3 long simple setae apically; outer plate with a row of long simple setae on lateral and apical margins. Pereion ( Figures 2d , 15a, b , 16a–e ). Gnathopod I carpus (article 5) 0.6× as long as propodus, rastellate setae absent; palm oblique, defining angle indistinct, palm with cutting margin crenulated, palm with 13 distally notched robust spines in two rows; dactylus, inner margin dentate, with 1 seta along outer margin. Gnathopod II carpus (article 5) slightly longer than propodus, rastellate setae absent; propodus palm bevelled, defining angle distinct, palm with cutting margin crenulated, palm with 5 distally notched robust setae in two rows and 7 distally notched robust setae near defining angle; dactylus similar to that of gnathopod I. Pereopods III and IV sub-similar; bases sub-linear, with a row of long and short setae on posterior margin; carpus (article 5) as long as propodus, posterior margin naked. Pereopod VI as long as pereopod VII . Ventral surface of pereonites II–VII bearing sternal humps (blisters). Coxal gills II–VI stalked and saccular. Oostegites II–V on gnathopod II and pereopods III–V developed, without marginal setae. Pleon ( Figures 2d , 17a–h ). Epimera I–III (pleonal plates) posterior corners broadly roundish, armed with 1 stiff seta each; ventral margin of plate I without setae, plates II and III with 1 seta each. Pleopods I–III peduncular articles with 2 coupling setae (retinacles). Uropod I peduncle with 5 spines on outer margin, 3 spines on inner margin, 1 basofacial spine-seta; outer ramus 0.6× as long as inner ramus, about 50% length of peduncle; inner ramus armed with 6 spines on each margin and with 4 long thin setae on ventral face; outer ramus unarmed; rami with 5 spines on apices, one or two of them very long. Uropod II peduncle with 2 spines on outer margin and 3 spines on inner margin; outer ramus 0.8× as long as inner ramus; inner ramus as long as peduncle, armed with spines on both margins; outer margin of outer ramus with 2 spines; rami with 5 spines on apices, one or two of them long. Uropod III uniramous; peduncle with 1 spine and 1 seta on distal margin; proximal article of outer ramus 3.0× as long as peduncle, bearing 4 sets of spines on inner and outer margins; terminal article 0.2× as long as proximal article, with 3 setae on apex. Telson 1.4× as long as uropod III peduncle; 0.5× longer than broad, apical margin with vestigial notch; tips of lobes with 1 long spine apically each.