Pseudocrangonyx danyangensis, Lee & Min, 2024

Lee, Chi-Woo & Min, Gi-Sik, 2024, Two new species of Pseudocrangonyx (Amphipoda: Pseudocrangonyctidae) from the hyporheic zones in South Korea, Zootaxa 5433 (2), pp. 249-265 : 258-264

2. Pseudocrangonyx danyangensis sp. nov.

urn:lsid:zoobank.org:act:514F443E-A246-4FFF-91B0-0540090CC498

[New Korean name: dan-yang-dong-gul-yeop-sae-u]

( Figs. 2B , 7–10 )

Material examined. Holotype: NNIBRIV69645, female, BL 5.2 mm, collected from Namhan River (37°5.063′N, 128°29.043′E), Yeongchun-myeon, Danyang-gun, Chungcheongbuk-do, Korea, on 19 Jun 2020, by C. -W. Lee.

Paratypes: NNIBRIV69646, 1 male, BL 4.0 mm, NNIBRIV69644, 1 female, BL 4.9 mm; collection data same as for holotype .

Diagnosis. Antennal sinus with rounded angle; eyes absent; pereonites 1–7 with short dorsal setae; dorsal margin of urosomite 1–3 with setae; sternal gill absent; antenna 1 being 0.38 times as long as body length; male antenna 2 with calceoli; maxilla 1 outer plate with 7 serrate teeth; maxilla 2 inner plate with oblique inner row of 2 setae; palmar margins of propodi of gnathopods 1 and 2 with 5–6 and 7 robust setae, respectively; pleopods inner margin of inner rami with bifid setae; uropod 1 inner ramus 0.74 times as long as peduncle, inner margin with 2 robust setae, outer margin bare, basal part with 2 slender setae, outer ramus 0.67 times as long as inner, inner margin and marginal with robust seta, respectively; uropod 2 peduncle outer and inner margin with 6 and 2 robust setae, respectively; uropod 3 terminal article longer than adjacent robust setae; telson each lobe with 2 lateral penicillate setae, 1 apical robust and 1 apical penicillate seta.

Description. Female holotype (NNIBRIV69645): Head ( Fig. 2B ) with short dorsal setae; rostrum reduced; lateral cephalic lobe rounded; antennal sinus shallow with rounded angle; eyes absent. Dorsal margin of pleonites 1–7 and urosomites 1–2 with setae ( Fig. 2B ). posteroventral corner of urosomite 1 with seta ( Fig. 2B ). Ventral margin of epimeral plate 1 without seta, posteroventral corner rounded with seta ( Fig. 2B ); ventral and posterior margins of plate 2 each with seta, posteroventral corner rounded with seta ( Fig. 2B ); ventral and posterior margins of plate 3 each with 2 setae, posteroventral corner rounded without seta ( Fig. 2B ).

Antenna 1 ( Fig. 7A ) 0.38 times as long as body length, peduncular articles 1 to 3 in length ratio of 1.0: 0.6: 0.34; accessory flagellum ( Fig. 7B ) 2-articulate, terminal article with 3 setae and 1 aesthetasc; primary flagellum 11- articulate, 1 aesthetasc on some articles. Antenna 2 ( Fig. 7C ) 0.65 times as long as antenna 1; flagellum 0.69 times as long as peduncular articles 4 and 5 combined, consisting of 5 articles; calceoli absent.

Upper lip ( Fig. 7D ) with rounded anterior margin, bearing fine setae. Mandibles ( Fig. 7E, F ) with left and right incisors with 6- and 4- dentate, respectively; left lacinia mobilis 5- dentate, right lacinia bifid, bearing many teeth; molar process triturative; palp 3-articulate, article 3 with 1 A-, 5 D-, and 4 E-setae. Lower lip ( Fig. 7G ) with broad outer lobes with fine setae, mandibular process of outer lobe rounded apically; inner lobes indistinct. Maxilla 1 (Male paratype, Fig. 7H ) with inner and outer plates, and palp; inner plate subovate with 3 plumose setae; outer plate subrectangular with 7 serrate teeth apically; palp 2-articulate, longer than outer plate, article 2 with 3 apical robust setae. Maxilla 2 ( Fig. 7I ) with oblique inner row of 2 setae on inner plate. Maxilliped ( Fig. 7J ) with inner and outer plates, and palp; inner plate with apical robust seta; outer plate with plumose seta and some medial setae; palp 4-articulate, medial margin of article 2 lined with setae, article 4 with nail.

Gnathopod 1 ( Fig. 8A ) with subquadrate coxa, bearing setae on anterodistal corner and margin, width 1.8 times as long as depth; posterior margin of basis with 3 setae; posterodistal corner of carpus with slender setae, some weakly pectinate; propodus stout, subtriangular, palmar margin with 5 robust setae, some distally notched; posterior margin of dactylus dentate. Gnathopod 2 ( Fig. 8B ) with subquadrate coxa, bearing setae on anterodistal corner and posteroventral margin, width 1.6 times as long as depth; posterior margin of basis with 4 setae; posterodistal corner of carpus with slender setae, some weakly pectinate; propodus stout, subchelate, palmar margin with 7 robust setae, some distally notched; posterior margin of dactylus dentate.

Pereopod 3 ( Fig. 8C ) with subquadrate coxa bearing setae on anterior to posteroventral margins, width 1.6 times as long as depth; anterior and posterior margins of basis with 2 and 4 setae, respectively; merus, carpus, and propodus in length ratio of 1.0: 0.7: 0.8; posterior margin and submargin of dactylus each with seta ( Fig. 8D ). Pereopod 4 ( Fig. 8E ) with subquadrate coxa bearing setae on anterior to ventral corner, width 1.86 times as long as depth; anterior and posterior margins of basis each with 3 and 4 setae; merus, carpus, and propodus in length ratio of 1.0: 0.8: 0.8; posterior margin and submargin of dactylus each with seta ( Fig. 8F ). Pereopod 5 ( Fig. 8G ) with weakly bilobed coxa bearing setae on anterior to posterior lobes; anterior and posterior margins of basis with 3 setae, respectively; merus, carpus, and propodus in length ratio of 1.0: 0.7: 0.8; anterior margin of dactylus with seta ( Fig. 8H ).

Pereopod 6 ( Fig. 8I ) with weakly bilobed coxa bearing setae on posterior lobe; anterior and posterior margins of basis with 4 and 2 setae, respectively; merus, carpus, and propodus in length ratio of 1.0: 0.7: 0.9; anterior margin of dactylus with seta ( Fig. 8J ). Pereopod 7 ( Fig. 8K ) with subtriangular coxa, bearing seta on posteroproximal corner; anterior and posterior margins of basis with 3 setae, respectively; merus, carpus, and propodus in length ratio of 1.0: 0.9: 1.1; anterior margin of dactylus with seta ( Fig. 8L ).

Coxal gills ( Fig. 8B, C, E, G, I ) on gnathopod 2 and pereopods 3–6; sternal gills absent. Brood plates ( Fig. 8C, E, G ) slender, with numerous setae, on gnathopod 2 and pereopods 3–5.

Peduncles of pleopod 1 and 2 ( Fig. 9A, B ) anterodistal corner with seta; peduncle of pleopod 3 ( Fig. 9C ) with marginal setae. Pleopods 1–3 with paired retinacula, and with bifid seta (clothes-pin setae) on inner basal margin of inner ramus; pleopods 1–3 inner ramus 4-, 3-, and 3-articulate; pleopods 1–3 outer ramus 5-, 4-, and 3-articulate ( Fig. 9A–C ).

Uropod 1 ( Fig. 9D ) with 2 basofacial setae on peduncle; inner ramus 0.74 times as long as peduncle, inner margin with 2 robust setae, outer margin bare, basal part with 2 slender setae; outer ramus 0.67 times as long as inner, inner margin and marginal with robust seta, respectively. Uropod 2 ( Fig. 9E ) with inner and outer rami; peduncle outer and inner margin with 6 and 2 robust setae, respectively; inner ramus 0.76 times as long as peduncle, inner margin with 2 robust setae; outer ramus 0.73 times as long as inner ramus, marginally bare. Uropod 3 ( Fig. 9F ) with peduncle 0.32 times as long as outer ramus, with 2 robust and 1 slender setae; inner ramus absent; outer ramus 2-articulate, proximal article with robust setae, terminal article 0.38 times as long as proximal article, with 3 distal setae.

Telson ( Fig. 9G ) length 1.53 times as long as wide, almost not cleft, each telson lobe with 2 lateral penicillate setae, 1 apical robust and 1 apical penicillate seta.

Male paratype (NNIBRIV69646): Antenna 1 ( Fig. 10A, B ) 0.34 times as long as body length, primary flagellum 10-articulate, 1 aesthetasc on some articles. Antenna 2 ( Fig. 10C ) 0.73 times as long as antenna 1; flagellum 0.66 times as long as peduncular articles 4 and 5 combined, consisting of 4 articles, first 2 of which with calceoli.

Gnathopod 1 ( Fig. 10D ) with coxa width 1.94 times as long as depth; palmar margin with 6 robust setae in 2 rows, some distally notched. Gnathopod 2 ( Fig. 10E ) with coxa width 1.6 times as long as depth; palmar margin with 7 robust setae in 2 rows, some distally notched.

Uropod 1 ( Fig. 10F ) with basofacial seta on peduncle; inner ramus 0.78 times as long as peduncle, outer margin with 2 robust setae, inner margin bare, basal part with slender seta; outer ramus 0.71 times as long as inner ramus, inner margin with robust seta. Uropod 2 ( Fig. 10G ) with inner and outer rami; peduncle outer and inner margin with 7 and 2 robust setae, respectively; inner ramus 0.75 times as long as peduncle, inner and outer margins with 1 and 2 robust setae, respectively; outer ramus 0.83 times as long as inner ramus. Uropod 3 ( Fig. 10H ) with peduncle 0.32 times as long as outer ramus; inner ramus absent; outer ramus 2-articulate, proximal article with robust setae, terminal article 0.39 times as long as proximal article, with 3 distal setae.

Telson ( Fig. 10I ) length 1.45 times as long as width, subrectangular, almost not cleft.

Distribution. Known only from the type locality.

Etymology. The specific name is an adjective derived from Danyang-gun, the type locality of the new species.

Remarks. Pseudocrangonyx danyangensis sp. nov. is morphologically most similar to P. daejeonensis Lee et al., 2018 in having 1) antenna 1 length shorter than body length half, 2) antenna 1 accessory flagellum first article exceed main flagellum first article, 3) male antenna 2 with calceoli, 4) uropod 2 outer ramus marginally bare, 5) uropod 3 terminal article longer than adjacent robust setae, and 6) telson lobe with 2 lateral penicillate setae. However, the new species is distinguished from P. daejeonensis by the following features (features of P. daejeonensis in parentheses): 1) inner rami of pleopods with (without) bifid setae on inner margin, 2) female and male uropod 1 margin with (without) robust setae, 3) female uropod 2 peduncle shorter (longer) than inner ramus, 4) male uropod 2 peduncle outer margin with 7 (1 robust setae) robust setae, and 5) telson (cleft for 8.6% of length) almost not cleft.

The new species is also similar to P. seomjinensis sp. nov. in having 1) eyes completely absent, 2) maxilla 2 with oblique inner row of 2 setae on inner plate, 3) uropod 1 with same number robust setae, and 4) uropod 2 outer ramus marginally bare. However, P. danyangensis sp. nov. is distinguished from P. seomjinensis sp. nov. by following features (features of P. seomjinensis sp. nov. in parentheses): 1) antenna 1 accessory flagellum first article exceed (not exceed) main flagellum of first article, 2) inner rami of pleopods with (without) bifid setae on inner margin, 3) female uropod 2 peduncle outer margin with 6 robust setae (2 robust setae), 4) male uropod 2 outer ramus almost reach (shorter than) inner ramus end, and 5) male telson shape subrectangular (subtriangular).

Phylogenetic position and genetic distances. Phylogenetic relationships within Korean pseudocrangonyctid species were identified using 28S rRNA and COI gene sequences. The uncorrected COI p -distance between the two new species ( P. seomjinensis sp. nov. and P. danyangensis sp. nov.) was 15.2%, calculated based on 609 aligned positions from the dataset. This distance is the range of COI differentiation that can distinguish a distinct species in the genus Pseudocrangonyx , as reported previously ( Zhao & Hou 2017).

In phylogenetic analyses, the topologies of the BI and ML trees were almost identical.The molecular phylogenetic tree ( Fig. 11 ; ML tree not shown) showed that the Korean Pseudocrangonyx split into two clades: interstitial water (in the gray circle, P. daejeonensis Lee et al., 2018 ; P. seomjinensis sp. nov.; P. danyangensis sp. nov.) and cave groundwater (in the gray square, P. joolaei Lee et al., 2020 ; P. wonkimi Lee et al., 2020 ; P. deureunensis Lee & Min, 2021 ; P. kwangcheonseonensis Lee & Min, 2021 ; P. hwanseonensis Lee & Min, 2021 ) clades. Moreover, the obtained phylogenies revealed that the Korean interstitial water species are close congeners of the Japanese species ( P. uenoi Tomikawa & Nakano, 2019 and P. dunan Tomikawa et al., 2022 ) and are not Korean cave-dwelling species. Meanwhile, the Korean cave-dwelling species formed a clade with the Japanese P. akatsukai Tomikawa & Nakano, 2018 , which are morphologically similar. These relationships suggest that evolutionary history may have changed depending on the habitat environment, interstitial water, or cave groundwater. The Korean and Japanese Pseudocrangonyx may have diverged from a common ancestor.

Finally, the existence of pseudocrangonyctids is related to biogeographic interest, and the origin and evolution of subterranean amphipod fauna in the Far East region ( Sidorov & Holsinger 2007). Further taxon sampling and molecular data are required to elucidate the origin and dispersal routes of the genus Pseudocrangonyx ( Lee et al. 2018) . Further molecular phylogenetic analyses of Pseudocrangonyx will provide a better understanding of the diversity and evolutionary history of subterranean Crangonyctoidea species in Far East Asia.

Figures

FIGURE 2. Habitus of two new species. A, Pseudocrangonyx seomjinensis sp. nov.; B, Pseudocrangonyx danyangensis sp. nov..

FIGURE 7. Pseudocrangonyx danyangensis sp. nov., holotype female, NNIBRIV69645. A–G, I, J; paratype male, NNIBRIV69646, H. A, antenna 1, medial view; B, accessory flagellum of antenna 1, medial view; C, antenna 2, medial view; D, upper lip, posterior view; E, left mandible, medial view; F, incisor, lacinia mobilis of right mandible, medial view; G, lower lip, dorsal view; H, maxilla 1, dorsal view; I, maxilla 2, dorsal view; J, maxilliped, ventral view.

FIGURE 8. Pseudocrangonyx danyangensis sp. nov., holotype female, NNIBRIV69645. A, gnathopod 1, lateral view; B, gnathopod 2, lateral view; C, pereopod 3, lateral view; D, dactylus of pereopod 3, lateral view; E, pereopod 4, lateral view; F, dactylus of pereopod 4, lateral view; G, pereopod 5, lateral view; H, dactylus of pereopod 5, lateral view; I, pereopod 6, lateral view; J, dactylus of pereopod 6, lateral view; K, pereopod 7, lateral view; L, dactylus of pereopod 7, lateral view.

FIGURE 9. Pseudocrangonyx danyangensis sp. nov., holotype female, NNIBRIV69645. A–C, Pleopod 1–3, lateral view; D, uropod 1, ventral view; E, uropod 2, dorsal view; F, uropod 3, dorsal view; G, telson, ventral view.

FIGURE 10. Pseudocrangonyx danyangensis sp. nov., paratype male, NNIBRIV69646.A, antenna 1, medial view; B, accessory flagellum of antenna 1, medial view; C, antenna 2, lateral view; D, gnathopod 1, lateral view; E, gnathopod 2, lateral view; F, uropod 1, ventral view; G, uropod 2, ventral view; H, uropod 3, dorsal view; I, telson, ventral view.

FIGURE 11. Maximum likelihood and Bayesian inference analyses based on nuclear 28S rRNA and mitochondrial COI sequences. Numbers on nodes represent bootstrap values for maximum likelihood and Bayesian posterior probabilities.