Pseudocrangonyx gudariensis Tomikawa & Sato

Tomikawa, Ko, Nakano, Takafumi, Sato, Anna, Onodera, Yutaka & Ohtaka, Akifumi, 2016, A molecular phylogeny of Pseudocrangonyx from Japan, including a new subterranean species (Crustacea, Amphipoda, Pseudocrangonyctidae), Zoosystematics and Evolution 92 (2), pp. 187-202 : 189-193

Taxon classification Animalia Amphipoda Pseudocrangonyctidae

Pseudocrangonyx gudariensis Tomikawa & Sato sp. n. Figs 2, 3, 4, 5, 6, 7, 8, 9

Pseudocrangonyx gudariensis New Japanese name: Gudarimekura-yokoebi

Type materials.

Holotype: Male (3.9 mm), NSMT-Cr 24603, Gudari-numa Stream (40°40'21.2″N, 140°55'54.6″E, elev. 589 m), Komagome, Aomori, Aomori Prefecture, Japan, 4 June 2014, collected by A. Ohtaka. Paratypes: 1 female (3.1 mm), NSMT-Cr 24604, locality same as for holotype, 21 June 2015, collected by A. Ohtaka; 1 female (4.4 mm), NSMT-Cr 24605, locality same as for holotype, 14 March 2015, collected by A. Ohtaka; 1 male (2.5 mm) and 3 females (1.4-2.8 mm), NSMT-Cr 24606, locality same as for holotype, 23 May 2015, collected by A. Ohtaka; 4 females (2.0-2.9 mm) KUZ Z1746, data same as for holotype, collected by A. Ohtaka.

Type locality.

Japan, Aomori Prefecture: Aomori, Gudari-numa Stream (northern Honshu).

Description.

Male [NSMT-Cr 24603, 3.9 mm]. Head (Fig. 2) with short dorsal setae; rostrum reduced; lateral cephalic lobe rounded; antennal sinus shallow with rounded angle; eyes absent. Pereonites 1-7 with short dorsal setae (Fig. 2); posterolateral margin of pereonites 5-7 with seta (Fig. 2). Dorsal margin of pleonites 1-3 with 5, 6, and 8 setae, respectively (Fig. 7 I–K). Dorsal margin of urosomites 1 and 2 each with 4 setae (Fig. 7L, M), dorsal margin of urosomite 3 lacking setae (Fig. 7N). Posterior margin of epimeral plate 1 with 2 setae, posteroventral corner rounded with 1 seta (Fig. 7P); ventral and posterior margins of plate 2 with 1 and 2 setae, respectively, posteroventral corner rounded, with 1 seta (Fig. 7Q); ventral and posterior margins of plate 3 each with 1 seta, posteroventral corner rounded, with 1 seta (Fig. 7R).

Antenna 1 (Fig. 3A) 0.47 times as long as body length, peduncular articles 1 to 3 in length ratio of 1.0: 0.6: 0.4; accessory flagellum 2-articulate, terminal article with 3 setae; primary flagellum 12-articulate, 1 aesthetasc on some articles. Antenna 2 (Fig. 3B) 0.60 times as long as antenna 1; peduncular article 5 with calceolus; flagellum 0.55 times as long as peduncular articles 4 and 5 combined, consisting of 4 articles, first 2 of which with calceolus.

Upper lip (= labrum) (Fig. 3C) with rounded anterior margin, bearing fine setae. Mandibles (Fig. 3E, F) with left and right incisors both 5-dentate; left lacinia mobilis 4-dentate, right lacinia bifid, bearing many teeth; molar process triturative, molar of right mandible with accessory seta; accessory setal rows of left and right mandibles with 3 and 2 weakly pectinate setae, respectively; palp 3-articulate, article 3 with 1 A-, 4-5 D-, and 4 E-setae. Lower lip (Fig. 3D) with broad outer lobes, mandibular process of outer lobe rounded apically; inner lobes indistinct. Maxilla 1 (Fig. 3G) with inner and outer plates, and palp; inner plate subovate, its medial margin with 3 plumose setae; outer plate subrectangular with 7 serrate teeth apically; palp 2-articulate, longer than outer plate, article 1 lacking marginal setae, article 2 with 3 apical and 1 subapical robust setae. Maxilla 2 (Fig. 3H) with oblique inner row of 3 plumose setae on inner plate. Maxilliped (Fig. 4 A–C) with inner and outer plates, and palp; inner plate (Fig. 4C) with 3 apical and 2 subapical robust setae; outer plate (Fig. 4B) with 1 apical plumose seta and 1 apical robust seta and 5 medial slender setae; palp (Fig. 4A) 4-articulate, medial margin of article 2 lined with setae, article 4 with nail.

Gnathopod 1 (= pereopod 1) (Fig. 4D, E) with subquadrate coxa, bearing setae on anterodistal corner of coxa, width 2.0 times as long as depth; anterior margin of basis bare, posterior margin of basis with 5 setae; posterodistal corner of carpus with slender setae, some weakly pectinate; propodus stout, subchelate, palmar margin with 6 medial and 5 lateral robust setae, some distally notched (Fig. 4E); posterior margin of dactylus dentate (Fig. 4E). Gnathopod 2 (= pereopod 2) (Fig. 4F, G) with subquadrate coxa bearing setae on its anterior margin and posterodistal corner, width 1.9 times as long as depth; anterior and posterior margins of basis with 0 and 5 setae, respectively; posterodistal corner of carpus with slender seta, some weakly pectinate; propodus stout, subchelate with 6 medial and 8 lateral robust setae along palmar margin, some distally notched (Fig. 4G); posterior margin of dactylus dentate (Fig. 4G). Pereopod 3 (Fig. 5A) with subquadrate coxa bearing setae on its anterodistal and and posteroventral corners, width 1.8 times as long as depth; anterior and posterior margins of basis with 2 and 5 setae, respectively; merus, carpus, and propodus in length ratio of 1.0: 1.0: 0.9; posterior margin of dactylus with 1 seta. Pereopod 4 (Fig. 5B) with subquadrate coxa bearing setae on its anterior margin, anterodistal and posteroventral corners, width 1.8 times as long as depth; anterior and posterior margins of basis each with 3 setae; merus, carpus, and propodus in length ratio of 1.0: 0.8: 0.8; posterior margin of dactylus with 1 seta. Pereopod 5 (Fig. 5C, D) with weakly bilobed coxa bearing setae on anterior and posterior lobes; anterior and posterior margins of basis with 3 and 4 setae, respectively; merus, carpus, and propodus in length ratio of 1.0: 0.8: 0.9; posterior margin of dactylus with 2 setae (Fig. 5D). Pereopod 6 (Fig. 6A, B) with coxa bearing concave lower margin, posteroproximal corner with 1 seta; anterior and posterior margins of basis with 4 and 3 setae, respectively; merus, carpus, and propodus in length ratio of 1.0: 0.9: 1.1; posterior margin of dactylus with 2 setae (Fig. 6B). Pereopod 7 (Fig. 6 C–E) with subtriangular coxa, bearing 1 seta on posteroproximal corner; anterior and posterior margins of basis each with 3 setae; merus, carpus, and propodus in length ratio of 1.0: 1.1: 1.2; posterior margin of dactylus with 2 setae (Fig. 6E).

Coxal gills (Fig. 2) on gnathopod 2 and pereopods 3-6; sternal gills absent.

Peduncles of pleopods 1 and 2 (Fig. 7A, C) with 2 and 1 setae on outer margins, respectively; peduncle of pleopod 3 (Fig. 7D) lacking marginal setae. Pleopods 1-3 each with paired retinacula (Fig. 7B), and lacking bifid setae (clothes-pin setae) on inner basal margin of inner ramus.

Uropod 1 (Fig. 7E) with basofacial slender seta on peduncle; inner ramus 0.70 times as long as peduncle, inner margin of former with 2 robust setae, outer margin bare, basal part with 3 slender setae; outer ramus 0.76 times as long as inner, its inner and outer margins with 0 and 2 robust setae, respectively. Uropod 2 (Fig. 7F, G) with inner and outer rami; inner ramus 0.90 times as long as peduncle, its inner margin with 4 robust setae, outer margin bare, distal part with 2 serrate and 4 simple robust setae and 1 slender seta (Fig. 7G); outer ramus 0.89 times as long as inner ramus, its outer margin with 1 robust seta. Uropod 3 (Fig. 7H) with peduncle 0.33 times as long as outer ramus, with 1 dorsal and 3 ventral robust setae; inner ramus absent; outer ramus 2-articulate, proximal article with robust setae, terminal article 0.36 times as long as proximal article, with 3 distal setae.

Telson (Fig. 7O) length 1.2 times as long as wide, cleft for 0.08 times of length, each telson lobe with 2 lateral long penicillate setae, 2 apical robust and 1 apical short penicillate setae.

Female [NSMT-Cr 24604, 3.1 mm]. Antenna 1 (Fig. 8A) 0.58 times as long as body length, primary flagellum 12-articulate. Antenna 2 (Fig. 8B) 0.64 times as long as antenna 1, calceoli absent; flagellum 0.64 times as long as peduncular articles 4 and 5 combined, 5-articulate, first 2 of which with 1 robust seta, lacking calceoli.

Lacinia mobilis of left mandible 5-dentate.

Gnathopod 1 (Fig. 8C, D) with coxa width 1.9 times as long as depth; palmar margin (Fig. 8D) with 4 medial and 4 lateral distally notched robust setae. Gnathopod 2 (Fig. 8E, F) with coxa width 1.8 times as long as depth; palmar margin (Fig. 8F) with 9 medial and 5 lateral robust setae, some distally notched.

Brood plates (Fig. 8G) slender, with numerous setae, on gnathopod 2 and pereopods 3-5.

Uropod 1 (Fig. 9A) with 3 robust setae on inner margin of inner ramus, basal part with 2 slender setae; outer ramus 0.80 times as long as inner. Uropod 2 (Fig. 9B) with 6 simple robust setae and 1 slender seta on distal part of inner ramus. Uropod 3 (Fig. 9C) with peduncle 0.32 times as long as outer ramus; terminal article of outer ramus 0.35 times as long as proximal article.

Etymology.

The specific name is an adjective derived from Gudari-numa, the type locality of the new species.

Distribution and habitat.

This species is known only from the type locality. The specimens were collected from interstitial water in the gravelly bottom. Water temperature of the habitat was stable and around 7°C throughout the year (Baba and Ohtaka unpublished).

Remarks.

Pseudocrangonyx gudariensis is morphologically similar to Pseudocrangonyx coreanus described from the Korean Peninsula. The deposited female paratypes of the latter species have calceoli on antenna 2 and pleopods without bifid setae on inner basal margin of inner ramus, which are features that were not mentioned in the original description (NSMT-Cr 13521-13522; Tomikawa and Onodera, personal observation).These two species share the following features: 1) relatively small body size (smaller than 6 mm), 2) eye completely absent, 3) carpus of gnathopod 2 without serrate robust setae on posterodistal corners, 4) outer margin or outer distal corner of pleopods 1 and 2 with setae, 5) inner basal margin of inner ramus of pleopods without bifid setae, and 6) small number of articles (less than 5) of rami of pleopods. However, Pseudocrangonyx gudariensis is distinguished from Pseudocrangonyx coreanus by the following features (features of Pseudocrangonyx coreanus in parentheses): 1) antenna 2 of female without calceoli (present); 2) palmar margins of gnathopods 1 and 2 with distally notched robust setae (absent); 3) inner margin of inner ramus of uropod 2 with 4 (0 or 1) robust setae; and 4) basal part of inner ramus of uropod 2 without slender seta (present).

Pseudocrangonyx gudariensis is also similar to Pseudocrangonyx febras from river basin of Primorye, Russia in having 1) relatively small body size (smaller than 6.5 mm), 2) eye completely absent, 3) palmar margins of gnathopods 1 and 2 with distally notched robust setae, 4) small number of articles (less than 6) of rami of pleopods, and 5) urosomite 1 without basal setae. However, Pseudocrangonyx gudariensis is distinguished from the latter by the following features (features of Pseudocrangonyx febras in parentheses): 1) carpus of gnathopod 2 without serrate robust setae on posterodistal cor ners (present), 2) peduncle of pleopods 1 and 2 with setae (absent), and 3) article 2 of uropod 3 longer (shorter) than setae on distal part of article 1.