Pseudocrangonyx borealis, Sídorov & Labay & Gontcharov, 2020

Sídorov, Dmitry, Labay, Vjacheslav & Gontcharov, Andrey, 2020, New species and records of the subterranean amphipod genus Pseudocrangonyx Akatsuka and Komai (Crustacea: Pseudocrangonyctidae), representing the northernmost distribution of the group, Journal of Natural History 54 (27 - 28), pp. 1759-1795 : 1778-1779

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.

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.

Figures

Figure 2. Habitus of examined specimens: (a) Pseudocrangonyx spangsbergi sp. nov., holotype, female, 5.5 mm; (b) Pseudocrangonyx setosus sp. nov., holotype, female, 5.5 mm; (c) Pseudocrangonyx myaochanicus sp. nov., holotype, female, 3.2 mm; (d) Pseudocrangonyx borealis sp. nov., holotype, female, 4.5 mm; (e) Pseudocrangonyx camtschaticus Birstein, 1955, female, 7.5 mm.

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.

Figure 15. Pseudocrangonyx borealis sp. nov., holotype MNHN-IU-2019-3173, female, 4.5 mm: (a) gnathopod I; (b) gnathopod II. Scale bar: 0.2 mm.

Figure 16. Pseudocrangonyx borealis sp. nov., holotype MNHN-IU-2019-3173, female, 4.5 mm: (a) pereopod III; (b) pereopod IV; (c) pereopod V; (d) pereopod VI; (e) pereopod VII. Scale bar: 0.2 mm.

Figure 17. Pseudocrangonyx borealis sp. nov., holotype MNHN-IU-2019-3173, female, 4.5 mm: (a) pleopod I; (b) pleopod II; (c) pleopod III; (d) epimera I–III; (e) uropod I; (f) uropod II; (g) uropod III; (h) telson. Scale bar: 0.2 mm.