Pseudocrangonyx wonkimi, Lee & Tomikawa & Min, 2020

Lee, Chi-Woo, Tomikawa, Ko & Min, Gi-Sik, 2020, A new cave amphipod, Pseudocrangonyx wonkimi sp. nov. (Crustacea, Amphipoda, Pseudocrangonyctidae), from the Korean Peninsula, ZooKeys 960, pp. 1-15 : 1

Pseudocrangonyx wonkimi sp. nov.

Material examined.

Holotype: Female (NNIBRIV35119, BL = 8.9 mm), South Korea, Jeollanam-do, Hampyeong-gun, Daedong-myeon, Yongseong-ri, Jungchangjin Cave (35°6.05'N, 126°31.99'E), 17.II.2017, Yong Gun Choi leg.

Paratypes: 1 male (NNIBRIV36158, BL = 8.3 mm), 1 female (NNIBRIV36157, BL = 8.9 mm), collection data same as for the holotype.

Diagnosis.

Female larger than male; antennal sinus with rounded angle; eyes absent; pereonites 3-5 with short dorsal setae; sternal gill absent; antenna 1 shorter than body length; antenna 2 with calceoli in both sexes; mandible palp article 3 longer than article 2; maxilla 1 inner plate with 4 plumose setae; maxilla 2 inner plate with oblique inner row of 4 setae; pleopod peduncles with anterodistal setae, inner margin of pleopods 1 and 2 inner rami with bifid setae; uropod 1 outer ramus with 2 marginal robust setae; uropod 3 terminal article of the outer ramus shorter than adjacent spines.; telson cleft for 25.0-27.4%.

Description.

Female (NNIBRIV35119, 8.9 mm). Head (Fig. 2 ) without setae; rostrum short; lateral cephalic lobe rounded; antennal sinus shallow with rounded angle; eyes absent. Pereonites 3-5 with short dorsal setae; dorsal margin of pereonite 7 with long setae. Dorsal margins of pleonites 1-3 with long setae (Fig. 2 ). Posterior margin and posteroventral corner of epimeral plate 1 each with seta; ventral and posterior margins of plate 2 with 3 and 4 setae, respectively, posteroventral corner with seta; ventral and posterior margins of plate 3 with 2 and 4 setae, respectively, posteroventral corner subquadrate with seta (Fig. 2 ). Dorsal margin of urosomites 1 and 2 with seta, urosomite 3 lacking dorsal setae. Ventral margin of urosomite 1 with seta (Fig. 2 ).

Antenna 1 (Fig. 3A ) 0.47 times as long as body length, peduncular articles 1-3 in length ratio of 1.0: 0.8: 0.4; accessory flagellum (Fig. 3B ) 2-articulate, terminal article with 2 setae and aesthetascs; primary flagellum 1.5 times as long as peduncular articles 1-3 combined, 19-articulate, 1 aesthetasc on some articles. Antenna 2 (Fig. 3C, D ) 0.65 times as long as antenna 1; peduncular article 5 with 2 calceoli; flagellum 0.53 times as long as peduncular articles 4 and 5 combined, consisting of 8 articles, flagellum articles 2-4 with calceolus.

Upper lip (Fig. 3E ) with rounded anterior margin, with fine setae. Mandibles (Fig. 3F-H ) with left and right incisors 5-dentate; left lacinia mobilis 5-dentate, right lacinia bifid, with many teeth; molar process triturative; accessory setal rows of left and right mandibles each with 5- and 4- pectinate setae; palp 3-articulate, article 3 with 2 A-, 14 D-, and 3 E-setae. Lower lip (Fig. 3J ) with broad outer lobes with fine setae, mandibular process of outer lobe rounded apically; inner lobes indistinct. Maxilla 1 (Fig. 3K, L ) with inner and outer plates, and palp; inner plate subquadrate with 4 plumose setae; outer plate subrectangular with 7 serrate teeth apically; palp 2-articulate, longer than outer plate, article 2 with weakly plumose 3 apical and 4 subapical robust setae. Maxilla 2 (Fig. 3M ) with oblique inner row of 4 setae on inner plate. Maxilliped (Fig. 4A ) with inner and outer plates, and palp; inner plate with 3 apical robust setae; outer plate with 6 apical plumose setae, 3 subapical robust setae, and some medial setae; palp 4-articulate, medial margin of article 2 lined with setae, article 4 with claw.

Gnathopod 1 (Fig. 4B, C ) with subrectanqular coxal plate, bearing setae on anterior margin and anterodistal corner, width 1.7 times as long as depth; basis thick and short, anterior margin bare, submargin with setae, posterior margin with 7 long setae; posterodistal corner of carpus with serrate robust seta; propodus stout, subtriangular, palmar margin with 14 robust setae in 2 rows, some distally notched; posterior margin of dactylus dentate (Fig. 4D ). Gnathopod 2 (Fig. 4E, F ) with rounded subquadrate coxal plate, with setae on its anterior to ventral margins, width 1.3 times as long as depth; basis slender with short setae on anterior margin, posterior margin with 8 long setae; posterodistal corner of carpus with serrate robust seta; propodus more slender than that of gnathopod 1, palmar margin with 14 robust setae in 2 rows, some distally notched; posterior margin of dactylus dentate (Fig. 4G ).

Pereopod 3 (Fig. 5A ) with subquadrate coxal plate bearing setae on anterior to ventral margins, width 1.5 times as long as depth; anterior and posterior margins of basis with short and long setae, respectively; merus, carpus, and propodus in length ratio of 1.0: 0.7: 0.7; posterior margin of dactylus with 2 setae (Fig. 5B ). Pereopod 4 (Fig. 5C ) with subquadrate coxal plate bearing setae on anterior to ventral margins, width 1.7 times as long as depth; anterior and posterior margins of basis with setae; merus, carpus, and propodus in length ratio of 1.0: 0.8: 0.8; posterior margin of dactylus with 2 setae (Fig. 5D ). Pereopod 5 (Fig. 5E ) with weakly bilobed coxal plate bearing setae on anterior to posterior lobes; anterior and posterior margins of basis with setae; merus, carpus, and propodus in length ratio of 1.0: 0.8: 0.8; anterior margin of dactylus with 2 setae (Fig. 5F ). Pereopod 6 (Fig. 5G ) with weakly bilobed coxal plate bearing setae on posterior lobes; anterior and posterior margins of basis with setae; merus, carpus, and propodus in length ratio of 1.0: 0.9: 0.9; anterior margin of dactylus with 2 setae (Fig. 5H ). Pereopod 7 (Fig. 5I ) with posteriorly tapering coxal plate, ventral margin weakly concave, with seta on posterodistal corner; anterior and posterior margins of basis with short setae; merus, carpus, and propodus in length ratio of 1.0: 1.0: 1.0; anterior margin of dactylus with 2 setae (Fig. 5J ).

Coxal gills (Fig. 4E , 5A, C, E, G ) on gnathopod 2 and pereopods 3-6; sternal gills absent.

Brood plates (Fig. 4E , 5A, C, E ) slender with numerous setae, on gnathopod 2 and pereopods 3-5.

Peduncles of pleopods 1-3 (Fig. 6A, C, E ) lacking marginal setae, anterodistal corners with 2 setae. Pleopods 1-3 with paired retinacula (Fig. 6B, D, F ). Pleopods 1 and 2 with bifid seta (clothes-pin seta) on inner basal margin of inner ramus; pleopods 1-3 inner ramus 7-, 7-, and 5-articulate, respectively; pleopods 1-3 outer ramus 8-, 7-, and 5-articulate, respectively.

Uropod 1 (Fig. 6G ) with basofacial seta on peduncle; inner ramus 0.7 times as long as peduncle, inner and outer margins with 3 and 2 robust setae, respectively, basal part with 4 slender setae; outer ramus 0.8 times as long as inner ramus, with 2 outer marginal robust setae. Uropod 2 (Fig. 6H ) with inner ramus 1.1 times as long as peduncle, inner and outer margins each with 2 robust setae; outer ramus 0.7 times as long as inner ramus, with 2 outer marginal robust setae, respectively. Uropod 3 (Fig. 6I, J ) with peduncle 0.3 times as long as outer ramus; inner ramus absent; outer ramus 2-articulate, proximal article with robust setae, terminal article 0.1 times as long as proximal article, with 3 distal setae.

Telson (Fig. 6K ) length 1.57 times as long as wide, cleft for 25.0% of its length, each telson lobe apical with penicillate seta and 2 robust setae.

Male (NNIBRIV36158, BL = 8.3 mm). Antenna 1 (Fig. 7A, B ) 0.36 times as long as body length, primary flagellum 14-articulate, 1 aesthetasc on some articles. Antenna 2 (Fig. 7C ) 0.66 times as long as antenna 1; flagellum 0.33 times as long as peduncular articles 4 and 5 combined, consisting of 5 articles, articles 1 and 2 with calceolus.

Gnathopod 1 (Fig. 7D ) carpus with serrate seta on posterodistal corner; palmar margin of propodus with 10 robust setae in 2 rows, some distally notched. Gnathopod 2 (Fig. 7E ) carpus with serrate seta on posterodistal corner; palmar margin of propodus with 11 robust setae in 2 rows, some distally notched.

Uropod 1 (Fig. 8A ) with inner ramus 0.7 times as long as peduncle; inner and outer margins with 2 and 1 robust setae, respectively, basal part with 2 slender setae; outer ramus with 2 marginal robust setae. Uropod 2 (Fig. 8B ) with peduncle 0.95 times as long as inner ramus; inner ramus 1.4 times as long as outer ramus, distal part with 3 serrate, 4 simple robust setae. Uropod 3 (Fig. 8C, D ) with outer ramus terminal article 0.2 times as long as proximal article.

Telson (Fig. 8E ) length 1.38 times as long as wide, cleft for 27.4% of its length.

Distribution.

Known only from the type locality.

Etymology.

The name of the new species is dedicated to Prof. Won Kim (Seoul National University, South Korea), who has significantly contributed to our knowledge of crustaceans in South Korea.

DNA sequences.

Sequences of COI gene (MT316534 and MT316535) were determined from two specimens (NNIBRIV35119 and NNIBRIV36158).

Molecular analyses.

The topologies of the BI and ML trees were identical (Fig. 9 ). Pseudocrangonyx wonkimi sp. nov. and P. joolaei Lee et al., 2020 showed the closest relationship.

Remarks.

We revealed that Pseudocrangonyx wonkimi sp. nov. is most closely related to P. joolaei Lee et al., 2020 based on molecular analyses. The genetic distance between these two species was 15.1% for the COI gene, and this distance is larger than that between members of two distinct species among the other congeners examined. Pseudocrangonyx wonkimi sp. nov. is distinguished from P. joolaei in having the following features (features of P. joolaei in parentheses): 1) sternal gill absent (present), 2) maxilla 1 inner plate with 4 (6) plumose setae, 3) carpus of gnathopods 1 and 2 each with serrate robust seta (with 2-3) on the posterodistal corner, 4) inner basal margin of inner rami of pleopod 3 without (with) bifid seta, and 5) less than 10 (more than 10) articles on the rami of pleopods.

Pseudocrangonyx wonkimi sp. nov. is morphologically similar to P. akatsukai Tomikawa & Nakano, 2018 in having 1) eyes completely absent, 2) sternal gill absent 3) urosomite 1 with ventral robust seta, 4) antenna 2 with calceoli in both sexes 5) carpi of gnathopods 1 and 2 with serrate robust setae on posterodistal corner, and 6) inner rami of pleopods with bifid setae on inner margin. However, the former is distinguished from the latter by the following features (features of P. akatsukai in parentheses): 1) pereonites 3-5 (1-7) with short dorsal setae, 2) antenna 1 shorter (longer) than as long as body length half, 3) male antenna 2 flagellum 0.33 (0.53) times as long as peduncular articles 4 and 5 combined, 4) carpi of gnathopods 1 and 2 with 1 (with 3-5) serrate robust setae on posterodistal corner, 5) length ratio of merus, carpus, propodus 1.0: 1.0: 1.0 (1.0: 1.1: 1.1) of pereopod 7, and 6) telson cleft for 25.0-27.4% (6.6-12.3%) of length.

Pseudocrangonyx wonkimi sp. nov. is similar to P. elegantulus Zhao & Hou, 2017 in having 1) urosomite 3 dorsal margin without seta, 2) sternal gill absent, 3) accessory flagellum of antenna 1 subequal first article of primary flagellum, and 4) antenna 2 with calceoli in both sexes. However, P. wonkimi is distinguished from the latter by the following features (features of P. elegantulus in parentheses), 1) pereonites 3-5 with (1-6 without) dorsal margin setae, 2) basal part of inner ramus of female uropod 1 with 4 (1) slender setae, 3) uropod 1 peduncle inner marginal with 3 (1) robust setae, 4) terminal article of uropod 3 almost reaching (fully exceed) robust setae on the distal part of the proximal article, and 5) carpus of male gnathopod 2 with (without) serrate robust seta on posterodistal corner. Pseudocrangonyx wonkimi sp. nov. is similar to P. shikokunis Akatsuka & Komai, 1922 in having 1) eyes absent, 2) mandible palp article 3 longer than article 2, and 3) carpi of gnathopods 1and 2 with serrate setae on the posterodistal corners. The new species is distinguished from the latter by the following features (features of P. shikokunis in parentheses), 1) antenna 1 shorter (longer) than half of the body length, 2) maxilla 1 inner plate with 4 or fewer setae (with 5 setae), and 3) male telson cleft for 27.4% (11.7%) of length. The new species is similar also to P. cavernarius Hou & Li, 2003 in having 1) body size about 8.0 mm, and 2) maxilla 1 inner plate with 4 plumose setae. It differs from P. cavernarius Hou & Li, 2003 by the following features (features of P. cavernarius in parentheses), 1) antenna 2 calceoli present (absent), 2) mandible palp article 3 longer (shorter) than article 2, 3) urosomite 3 dorsal margin without (with) setae, and 4) telson each lobe with (without) setae.

Figures

Figure 2. Pseudocrangonyx wonkimi sp. nov., holotype, female (BL = 8.9 mm). Habitus, lateral view.

Figure 3. Pseudocrangonyx wonkimi sp. nov., holotype, female (BL = 8.9 mm): A-H, J-M paratype, female (BL = 8.9 mm): I. A Antenna 1, lateral view B accessory flagellum of antenna 1, lateral view C antenna 2, medial view D calceolus of antenna 2, medial view E upper lip, anterior view F right mandible, medial view G incisor and lacinia mobilis process of right mandible, medial view H incisor and lacinia mobilis process of left mandible, medial view I incisor process of left mandible, medial view J lower lip, dorsal view K maxilla 1, dorsal view L apical robust setae on outer plate of maxilla 1, dorsal view M maxilla 2, dorsal view.

Figure 4. Pseudocrangonyx wonkimi sp. nov., holotype, female (BL = 8.9 mm). A Maxilliped, dorsal view B gnathopod 1, lateral view C serrate seta on posterodistal corner of carpus of gnathopod 1, lateral view D palmar margin of propodus and dactylus of gnathopod 1, lateral view E gnathopod 2, lateral view F serrate seta on posterodistal corner of carpus of gnathopod 2, lateral view G palmar margin of propodus and dactylus of gnathopod 2, lateral view.

Figure 5. Pseudocrangonyx wonkimi sp. nov., holotype, female (BL = 8.9 mm). A Pereopod 3, lateral view B dactylus of pereopod 3, lateral view C pereopod 4, lateral view D dactylus of pereopod 4, lateral view E pereopod 5, lateral view F dactylus of pereopod 5, lateral view G pereopod 6, lateral view H dactylus of pereopod 6, lateral view I pereopod 7, lateral view J dactylus of pereopod 7, lateral view.

Figure 6. Pseudocrangonyx wonkimi sp. nov., holotype, female (BL = 8.9 mm). A, C, E Pleopods 1 - 3, lateral view, plumose setae on rami omitted B, D, F retinacula on peduncle of pleopod 1 - 3, lateral view G uropod 1, dorsal view H uropod 2, dorsal view I uropod 3, dorsal view J terminal article of uropod 3, dorsal view K telson, dorsal view.

Figure 7. Pseudocrangonyx wonkimi sp. nov., paratype, male (BL = 8.3 mm). A Antenna 1, medial view B accessory flagellum of antenna 1, medial view C antenna 2, medial view D gnathopod 1, lateral view E gnathopod 2, lateral view.

Figure 8. Pseudocrangonyx wonkimi sp. nov., paratype, male (BL = 8.3 mm). A Uropod 1, ventral view B uropod 2, ventral view C uropod 3, ventral view D terminal article of uropod 3, ventral view E telson, dorsal view.

Figure 9. Maximum likelihood and Bayesian inference analyses based on mitochondrial COI sequences. Numbers on nodes represent bootstrap values for maximum likelihood and Bayesian posterior probabilities.