Pseudocrangonyx myaochanicus, 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 : 1772-1775

Pseudocrangonyx myaochanicus sp. nov.

( Figures 2c , 11–13 )

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; urosomite I with 2 facial setae and urosomite II with 2 notched facial spines, ecdysial setae absent; interantennal lobe of head short, rounded, inferior antennal sinus sub-quadrate; antenna I about 50% length of body; coxal plates I– IV shallow, sub-rectangular (wider than deep), plates V – VII sub-triangular with broad anterior lobes; posterodistal corners of pleonal plates I– III broadly roundish; palp mandible article 3 with 1 B-seta, 6 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 armed; pereopod VII about 50% length of body . Uropod I with 1 basofacial spine-seta. Telson with vestigial notch. Body length 3.2 mm (♀).

Material examined

Holotype MNHN-IU-2019-3172: ♀ ca. 3.2 mm (oostegites developed, non-setose), RUSSIA, Khabarovsky Kray , Solnechny District , Myao-Chan mountain range, 8 km W of Gorny, Levaya Silinka River, hyporhea, 50.699850, 136.359167, elevation 713 m, leg. E.A. Makarchenko, 28 July 2006.

Etymology

Species named ‘ myaochanicus ’ (Latin), an adjective that refers to the Myao-Chan range where it was collected. Gender masculine.

Description

Female (body 3.2 mm long), MNHN-IU-2019-3172. Head ( Figures 2c , 11a–j ). Antenna I about 45% longer than antenna II; peduncular articles 1–3 in length ratio 1:0.6:0.4; primary flagellum with 14 articles; aesthetascs present. Antenna II peduncular articles 4 and 5 in length ratio 0.9:1; flagellum with 5 articles; calceoli absent, but with slender semitransparent, rod-like structures (probably aesthetascs). Left mandible incisor 5-dentate; lacinia mobilis 5-dentate; setal row with 3 serrate setae; palp mandible article 3 as long as article 2; article 3 with 1 B-seta, 6 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 broad, roundish. Upper lip without peculiarities. Maxilla I inner plate with 3 plumose setae; outer plate with 7 serrate spines; palp article 2 about 2.0× 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 4 long simple setae apically; outer plate with a row of long simple setae on lateral and apical margins. Pereion ( Figures 2c , 12a–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 8 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 and short setae on posterior margin; carpus (article 5) as long as propodus, posterior margin with seta. Pereopod VII dactylus with 2 stiff setae on inner margin. Coxal gills II–VI stalked and saccular. Oostegites II–V on gnathopod II and pereopods III–V developed, without marginal setae. Pleon ( Figures 2c , 13a–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 3 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 50% length of peduncle; inner ramus armed with 3 spines on inner margin and with 2 long thin setae on ventral face; outer ramus with 2 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 0.75× as long as inner ramus; inner ramus 1.2× as long as peduncle, armed with 3 spines on inner margin; outer margin of outer ramus with 2 spines; rami with 5 spines on apices, one of them long. Uropod III uniramous; peduncle with 4 spines on distal margin; proximal article of outer ramus 2.3× as long as peduncle, bearing 3 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; 0.3× longer than broad, apical margin with vestigial notch; tips of lobes with 2 spines 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 11. Pseudocrangonyx myaochanicus sp. nov., holotype MNHN-IU-2019-3172, female, 3.2 mm: (a) antenna I; (b) antenna II; (c) upper lip; (d) lower lip; (e) maxilla I; (f) outer plate of maxilla I; (g) left mandible; (h) right mandible; (i) maxilla II; (j) maxilliped. Scale bars: 0.2 mm.

Figure 12. Pseudocrangonyx myaochanicus sp. nov., holotype MNHN-IU-2019-3172, female, 3.2 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 13. Pseudocrangonyx myaochanicus sp. nov., holotype MNHN-IU-2019-3172, female, 3.2 mm: (a) uropod I; (b) uropod II; (c) uropod III; (d) telson; (e) pleopod I; (f) pleopod II; (g) pleopod III; (h) epimera I–III. Scale bars: 0.2 mm.