Pseudocrangonyx setosus, 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 : 1767-1769

Pseudocrangonyx setosus sp. nov.

( Figures 2b , 7–10 )

Diagnosis (both sexes)

Slender, medium-sized amphipod of typical pseudocrangonyctid habitus (sexual dimorphism pronounced, i.e. males smaller than females; antenna II short, bearing calceoli; metasomal segments with a few facial setae; uropod II sexually dimorphic with rami bearing 5 modified spines); 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 cluster of 8–12 fine facial setae each; urosomite I with 4 facial setae and urosomite II with 2 notched facial spines, ecdysial setae absent; interantennal lobe of head tapered, rounded, inferior antennal sinus sub-quadrate; antenna I about 45% length of body; coxal plates I– IV shallow, sub-rectangular (wider than deep), plates V – VI sub-triangular with broad anterior lobes, plate VII triangular, bearing 1 stiff seta; posterodistal corners of pleonal plates I– III broadly roundish; palp mandible article 3 with 2 Bsetae , 7 D-setae and 3 E-setae; molar of mandible well developed; propodus of gnathopod I somewhat larger than that of gnathopod II; carpus of pereopods III – IV with posterior margin armed; pereopod VII about 30% length of body . Uropod I with 1 basofacial spineseta. Telson with vestigial notch. Body length 5.5 mm (♀), 3.5–4.5 mm (♂♂).

Material examined

Holotype MNHN-IU-2019-3171: ♀ ca. 5.5 mm (oostegites developed, setose), RUSSIA, Sakhalin, Sakhalinskaya Oblast, Nogliksky District, Nabil’skij mountain range , Tym River basin, source of nameless spring, under moss, 50.753833, 143.283933, elevation 925 m,

leg. L.A. Prozorova, 2 August 2002. Paratypes 11/10-DAS: 3 ♂♂ measuring 3.5 mm each, 1 ♂ 4.5 mm, same data as for holotype .

Etymology

Species named ‘ setosus ’ (Latin), an adjective that refers to the unusually well-developed dorsal setae. Gender masculine.

Description

Female (body 5.5 mm long), MNHN-IU-2019-3171. Head ( Figures 2b , 7a–h ). Antenna I about 33% longer than antenna II; peduncular articles 1–3 in length ratio 1:0.5:0.4; primary flagellum with 17 articles; aesthetascs present. Antenna II peduncular articles 4 and 5 in length ratio 0.9:1; flagellum with 6 articles; calceoli absent, but with slender, semitransparent rod-like structures (probably aesthetascs). Right mandible incisor 5-dentate; lacinia mobilis bifurcate, with numerous small teeth; molar process triturative, without seta; palp mandible article 3 shorter than article 2; article 3 with 2 B-setae, 7 D-setae and 3 E-setae. Left mandible incisor 5-dentate; lacinia mobilis 5-dentate; setal row with 3 serrate setae. Lower lip inner lobes absent; mandibular process narrow. Upper lip without peculiarities. Maxilla I inner plate with 3 plumose setae; outer plate with 7 serrate spines; palp article 2 about 3.0× 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 2b , 8a–g ). Gnathopod I carpus (article 5) 0.4× as long as propodus, rastellate setae absent; palm oblique, defining angle indistinct, palm with cutting margin crenulated, palm with 14 distally notched robust spines in two rows; dactylus, inner margin dentate, with 1 seta along outer margin. Gnathopod II carpus (article 5) slightly shorter than propodus, rastellate setae absent; propodus palm bevelled, defining angle distinct, palm with cutting margin crenulated, palm with 7 distally notched robust setae in two rows and 5 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 setae on posterior margin; carpus (article 5) as long as propodus or slightly shorter, posterior margin with thin seta. Pereopod VII longer than pereopod VI. Coxal gills II–VI stalked and saccular. Oostegites II–V on gnathopod II and pereopods III–V developed, with long marginal setae. Pleon ( Figures 2b , 9a–h ). Epimera I–III (pleonal plates) posterior corners broadly roundish, armed with 1 stiff seta each; ventral margin of plate I without setae, plate II with 1 seta, plate III with 2 setae. Pleopods I–III peduncular articles with 2 coupling setae (retinacles). Uropod I peduncle with 4 spines on outer margin, 1 spine on inner margin, 1 basofacial spine-seta; outer ramus 0.6× as long as inner ramus, about 60% length of peduncle; inner ramus armed with 4 spines on inner face and with 4 long, thin setae on ventral face; outer ramus with 3 spines; rami with 5 or 6 spines on apices, one of them very long. Uropod II peduncle with 2 spines on outer margin and 1 spine on inner margin; outer ramus 0.7× as long as inner ramus; inner ramus 1.3× as long as peduncle, armed with 4 spines; outer ramus with 3 spines; rami with 4 or 5 spines on apices, one of them very long. Uropod III uniramous; peduncle with 3 spines on distal margin; proximal article of outer ramus 2.7× as long as peduncle, bearing 5 sets of spines on inner and outer margins; terminal article 0.2× as long as proximal article, with 3 setae on apex. Telson 1.55× as long as uropod III peduncle; 0.4× longer than broad, apical margin with vestigial notch; tips of lobes with 1 curved spine apically.

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 7. Pseudocrangonyx setosus sp. nov., holotype MNHN-IU-2019-3171, female, 5.5 mm: (a) antenna I; (b) antenna II; (c) right mandible; (d) left mandible; (e) maxilla I; (f) outer plate of maxilla I; (g) lower lip; (h) maxilliped. Scale bars: 0.2 mm.

Figure 8. Pseudocrangonyx setosus sp. nov., holotype MNHN-IU-2019-3171, female, 5.5 mm: (a) gnathopod I; (b) gnathopod II; (c) pereopod III; (d) pereopod IV; (e) pereopod V; (f) pereopod VI; (g) pereopod VII. Scale bar: 0.2 mm.

Figure 9. Pseudocrangonyx setosus sp. nov., holotype MNHN-IU-2019-3171, female, 5.5 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.

Figure 10. Pseudocrangonyx setosus sp. nov., paratype 11/10-DAS, male, 3.5 mm: (a) antenna II; (b) gnathopod I; (c) gnathopod II; (d) uropod I; (e) uropod II; (f) telson. Scale bars: 0.2 mm.